One Pixel, One Interaction, One Game: An Experiment in Minimalist

arXiv:2207.03827v1 [cs.HC] 8 Jul 2022

One Pixel, One Interaction, One Game

An Experiment in Minimalist Game Design

Pier Luca Lanzi

∗

[email protected]

Politecnico di Milano

Milano, Italy

Daniele Loiacono

daniele.loi[email protected]

Politecnico di Milano

Milano, Italy

Alberto Arosio

Digital Tales

Milano, Italy

Dorian Bucur

Universitá degli Studi di Milano

Milano, Italy

Davide Caio

CyberCoconut

Milano, Italy

Luca Cap ecchi

Politecnico di Milano

Milano, Italy

Maria Giulietta Cappelletti

Politecnico di Milano

Milano, Italy

Lorenzo Carnaghi

Politecnico di Milano

Milano, Italy

Marco Giuseppe Caruso

Politecnico di Milano

Milano, Italy

Valerio Ceraudo

Politecnico di Milano

Milano, Italy

Luca Contato

Rising Pixel

Gran Canaria, Canary Islands, Spain

Luca Cornaggia

Politecnico di Milano

Milano, Italy

Christian Costanza

Big Bang Pixel

Milano, Italy

Tommaso Grilli

Politecnico di Milano

Milano, Italy

Sumero Lira

Neotenia

Milano, Italy

Luca Marchetti

Studio Evil

Bologna, Italy

Giulia Olivares

Lola Slug

Milano, Italy

Barbara Pagano

Universitá degli Studi di Milano

Milano, Italy

Davide Pons

Politecnico di Milano

Milano, Italy

Michele Pirovano

Curiosity Killed the Cat

Bergamo, Italy

Valentina Tosto

AnotheReality

Milano, Italy

ABSTRACT

Minimalist game design was introduced a decade ago as a general

design principle with a list of key properties for minimalist games:

basic controls, simple but aesthetically pleasing visuals, interesting

player choices with vast possibility spaces, sounds that resonate

with the design. In this paper, we present an experiment we did

to explore minimalism in game using a bo ttom-up approach. We

invited a small group of professional game designers and a larger

group of game design students to participate in a seminal experi-

ment on minimalism in game design. We started from the most ba-

sic game elements: one pixel and one key which provide the least

amount o f information we can display and reasonably the most

elementary action players can perform. We designed a game that

starts with a black pixel and asks players to press a key w hen the

pixel turns white. This minimal game, almost a Skinner box, cap-

tures the essential elements of the mechanics o f games like “The

Impossible Game,” which asks players to do nothing more than

press a key at the right moment. We presented this game concept

to the professional game d esigners and challenged them to create

∗

Contact author.

other games with the least amount of player interaction and dis-

played information. We did not sp ecify any constraint (as usually

done in other contexts) and left them free to express their view of

minimalistic game design. We repeated the experiment with 100+

students attending a master-level course on video game design and

development at our institution. We then analyzed the creations

of t he two groups, discussing the idea of minimalistic design that

emerges from the submitted game concepts.

CCS CONCEPTS

• Applied computing → Computer games; • Hu man-centere d

computing → Interaction devices.

KEYWORDS

game design, game mechanics, player interaction, player experi-

ence

1 INTRODUCTION

Minimalism in games comes in a wide variety of forms [12]. In

tabletop games, it may be achieved through abstraction [2 8], the

complexity of rulesets [26], or a visual redesign, as in the recent

Lanzi and Loiacono, et al.

revamp of Uno decks [21, 27]. In video games, minimalism can

be introduced at visual level, at control level or at system level

[17, 18]. Minimalist video games can be visually abst ract and base d

on a stylized representations of a reference game world [1, 3]; of-

ten, visual abst raction is accompanied with minimal sound design

[22]. They may have simpliﬁed controls [14] that map into com-

plex behaviors [6, 24]. They may be based on minimalist systems

providing players with a limited numb er of interesting choices that

enable surprisingly deep gameplay. A decad e ago, Nealen et al. [17,

18] introduced the notion of Minimalist Game Design, discussing

the importance of self-imp osed, artiﬁcially designed constrains for

exploring new frontiers of gameplay. Over the last decade, the prin-

ciples of minimalist game design have been embraced by the in-

creasing number of game jams, organized all over the world, which

are inherently based on self-imposed, deliberate constrains [20, 23],

a major enabler of creativity in design [18].

In this paper, we analyze minimalist game design using a bot-

tom up approach. We did not surveyed existing games as [18], in-

stead we challenged professional and video game design students

to develop the most minimalist games they could think of and an-

alyze their creations. Our goal was twofold. We wanted to explore

minimalism in game design a decade after [17, 18] both from the

persp ective of professionals working in the industry and stu dents

who are approaching the ﬁeld. Furthermore, we wanted to create

a coll ection of examples of minimalist games that we could pro-

vide to future students as inspiration (a so rt of minimalist game

design sandbox to play with) fo r developing their own idea of min-

imalism. We designed the most basic game we could come up with

(involving just a pixel and an elementary interaction) and explored

level design in such extreme minimalist scenario. Initially, we in-

vited a small group of professional game designers to participate

in the experiment, receiving more than 20 concepts. We did not

enforce constraints as it usually happens during game jams. We

just provided them the description of our very basic game as in-

spiration to design other original games with the least amount of

player interaction and on-screen information. We asked them to

submit a brief concept describing the gameplay, the level design

principles, and the instructions to teach players how to play. Next,

we repeated the experiment by inviting the 100+ students attend-

ing the master-level video game design and development course at

our institution, receiving 100+ co ncepts. Finally, we analyzed the

submitted concepts and investigated the idea of minimalist game

design that emerges in the two subject groups, also with respect to

the seminal work of [17, 18].

2 BACKGROUND

Minimalism is an artistic movement that originated in the late 1950s

and developed throughout the 1960s. It is characterized b y extreme

austerity and simplicity that seek to uncover the essence of a sub-

ject by eliminating all non-essential parts of it. Initially primarily

focused on music and aesthetics, it has expanded its inﬂuence over

all sorts of media, and human activities [13], including videogames

[17, 18].

Videogames were born minimal out of necessity to deal wit h the

severe limitations of early hardware platforms [16]. As the techno-

logical resources were becoming practically limitless, minimalism

helped small independent companies deal with other, still existing,

time and labor limitations [18], b ecoming a distinctive stylistic ref-

erence for many indie games (e.g., [4, 5]). Minimalism is usually

associated with an idea of austerity, spareness, and simplicity. In

videogames, it has been used as a tool to search for the essence of

game deﬁnitions [11, 17] and proposed as a general design princi-

ple [8, 18].

Juul [11] analyzed seven game deﬁnitions from a variety of his-

torical and contemporary sources. His approach was inclusive [17]

and aimed at proposing a deﬁnition that consolidated well-established

and accepted knowledge. Juul [11] synthetized a list six elements

that are “necessary and suﬃcient for something to be a game”: (i)

rules, (ii) variable and quantitative outcomes, (iii) valorization of

outcome, (iv) player eﬀort , (v) player attachment to outcome, and

(vi) negotiable consequences. In contrast, Myers [17] took an exclu-

sive approach and eliminated what is not equally shared by all def-

initions. The result is a minimal list of four elements that deﬁned

games, (i) “prohibitive” rules or rules of denial, (ii) goals, including

the game’s winning conditions, (ii) o pposition, provided for exam-

ple by an antagonist, and (iv) representation, or a falseness that is

contrary to the real. The list is presented as a tool to identify what

should not considered a game. For example, Myers [17] ar gues that

crossword puzzles are not games since they do not have element

of opposition or an antagonist.

Nealen et al. [18] proposed Mini malist Game Design as a gen-

eral design principle to elicit the exploration of new directions in

design and gameplay by introducing self-imposed, deliberate con-

straints on the entire d esign and development process. Minimal-

ist games should b e based on essential mechanics, small rulesets,

narrow decision spaces, abstract aesthetics; at the same time, the

imposed constraints however should not limit the depth of p lay or

the possibility space [18].

Minimalist games are also laboratories to study the characteris-

tics of games in a smaller and more controlled environment. Irak-

sen et al. [8] proposed a toolset of techniques to evaluate the dif-

ﬁculty of game variants, t o balance games, to explore the game

space, and predict the likelihood of p layer achieving speciﬁc ﬁ-

nal scores. Their approach integrated several methods (e.g., auto-

matic p laytesting, Monte Carlo simulatio n, player modeling, and

survival analysis) and would have been diﬃcult to validate using

more complex games [8]. Accordingly, Iraksen et al . [ 8] used a

parametrized version of the minimalist game, Flappy Bird [19], as

an experimental laboratory to assess their methodology. Lankes

[15] used abstract visuals and gaze-based interaction to investi-

gate t he perceived quality of social communication towards ab-

stract non-player characters using a minimalist game with basic

mechanics.

3 ONE P IXEL, ONE INTERACTION, ONE

GAME

A white pixel is the minimum amount of information we can show

on-screen, and pressing a key (or a button) is the least interaction

we can ask players. Therefore, we can design a game where the

player must press a key when the p ixel turns white. The design of

a level depends on the rate at which the pixel lights up and how

long the pixel stays illuminated. For example, we can design a level

One Pixel, One Interaction, One Game

where the pixel turns oﬀ for one second and on for one second;

the next level could reduce the time the pixel stays on or when the

pixel is oﬀ. Alternatively, we could have a level where the time the

pixel stays on decreases as the level progresses; or a level with no

pattern whatsoever, in which the sw itch-oﬀ and switch-on times

are entirely random. Such a game is elementary, but from a me-

chanical point of view, it cap tures essential components of games

like “The Impossible Game" [5], which asks players to do nothing

more than to press a key to jump at the right time. We coul d change

the interaction pattern by simply asking the player to hold down

a key when the pixel is oﬀ and release it when the pixel is on, in

a sort of negative space of the original interaction model. “Foton-

ica” [25] has the same interaction model in which players hold the

key down t o run, release it to jump, and press it again to land. The

change in the interaction is small but holding the spacebar to run

and releasing it to jump makes the gameplay feel pretty diﬀerent.

We could replace the pixel stat es with sounds and ask the players

to press a key when they hear speciﬁc sounds or music and ask

players to press the key following the underlying rhythm. Simi-

larly, “The Impossible Game” uses rhythm t o help players under-

stand when to jump. Fol lowing the same principle, we can create

a small memory game: the white pixel lights up a given number

of times (for example, three times in sequence), and t hen players

must press the key for the same number of times.

4 AN EXPERIMENT IN MINIMALIST GAME

DESIGN

The literature exploring minimalist game design takes a top-down

approach and either propose it as a general design principle [8, 18]

or synthesizes what are the core features of minimalist games [ 11].

In our study, we decided to take a bottom-up approach and inves-

tigate what people already working in (or just approaching) the

ﬁeld view as minimalist game design. Accordingly, we contacte d a

group of professional game designers and challenged them to de-

velop the most minimalist games they could think of and analyze

their creations. We did not enforce any constraints as it usu ally

happens during game jams. We just tried to inspire them with some

minimalist games (the same described in Section 3) and asked them

to design other original games with the least amount of player in-

teraction and on-screen information. We asked them to submit a

brief concept describing the gameplay, the level design principles,

and the instructions to teach players how to play. Next, we invited

the 100+ students attending a master-level video game design and

development course at our institution by providing the same infor-

mation and form provided to the ﬁrst group of subjects. Overall,

we received 22 concepts from professional designers and 104 from

the master students.

5 STATISTICS

We analyzed t he submitte d concepts and labeled them based on

their genre. In part icu lar, given the limited number of concepts

and the high variety of ideas, we used high-level labels such as,

Action, Memory, Puzzle, Rhythm, Exploration, and Party. We also

label the games based on the skills they required (e.g., dexterity,

reaction time, coordination, memory), and whether (i) they were

single or multi player; (ii) they had a reactive or stateful gameplay,

that is, players’ actions coul d be based solely by the current game

state or also had to take into account previous states; (iii) they in-

volved some strategic thinking; (iv) they were organized as one

inﬁnite level or as a sequence of levels, or (v) they applied proce-

dural content generat io n. In terms of genre, 63% of the proposed

concepts were action games, 15% were memory games, 11% puz-

zles, 7% rhythm games. In terms of players’ abilities, 30% involved

some kind of dexterity, 2 7% quick reaction time, 23% some cogni-

tive ability, 17% memory, 8% involved story telling. Most games

were single players (93%) and only very few games (3%) required

strategic decision. 62% of the games were purely reactive, in that

players did not need to remember the eﬀect of previous actions;

whereas, 38% were stateful and asked the player to be aware of

how the play developed over time. In terms of level design, 55%

were based on a single level that would run until gameover, while

the remaining ones were organized as a series of separate levels;

80% of the games applied procedural content generation.

6 THE GAMES

The submitted game concepts oﬀered a wide variety of mechanics

and themes. In this section, we include a small subset of them that

we selected to provide a good overview of such a variety. They are

listed anonymously in alphabetical order to avoid any sort of bias.

3.. 2.. 1.. Go! Players have to ﬂy an aircraft, represented with a

pixel, collecting pixels that appear on the screen over time. The

pixel aircraft starts to the center-left side of the screen, follow-

ing a linear trajectory to the right side of the screen. If the player

does not press a key in around 0.75 seconds (corresponding to a

rhythm of 80bpm, or beats per minute), the aircraft starts follow-

ing a broad counterclockwise spiraling trajectory that w ill reduce

its radius over time until a three pixels radius is reached. Then

the aircraft will st ar t following a clockwise spiral of increasing ra-

dius. Players control the aircraft by pressing and releasing the key

rhythmically with a frequency of at least 80bp m, playing a sound

at each keystroke. The world is a toroid; when the aircraft exit the

screen from one side, it will re-enter from the oppo site side, main-

taining the same trajectory. The aircraft starts with four fu el units,

and this will d rop by one unit every ten seconds; when it reaches

zero, the game ends. Players must harvest the fuel pixels that ap -

pear on the screen and remain there for a limited time; when the

time is up, the fuel pixel will start ﬂashing before it disappears and

another pixel appears. The aircraft is also the game user interface.

A short ﬂash every two seconds means t hat the aircraft has three

fuel points; two ﬂashes indicate two remaining fuel points; three

ﬂashes warn players that just a single fuel unit remains. When the

aircraft has collected the last fuel pixel, it starts to ﬂash at a high fre-

quency while playing a piece of music composed of three sounds,

and it moves to a new starting position. Resources: three sounds,

two pixels, one key. Level Design: the game is a rhythm game, and

each level is carefully designed to play (if performed perfectly) to

a given melo dy (or rather a rhythm). Every level has a growing

diﬃculty represented by the pixels’ time to collect that decreases

with the next level, making it more diﬃcult to maintain the fuel.

Instructions: Fearless pilot! Press a button to turn the plane clock-

wise, release it to turn counterclockwise. Refuel by collecting ten

pixels and move to the next level. Let the pace be with you!

Lanzi and Loiacono, et al.

Aliens Attack from De ep Space. When the output system an-

nounces an alien presence (on a screen o r something else), the

player has little time to shoot and kill it. Resources: An input sys-

tem (a button, better if a trigger on a gun) and an ou tput system (a

pixel that turns on, a sound, a vibration). Level Design: aliens will

arrive with a random time ranging from 1 second to one minute,

such high variability aims at increasing players anxiety over the

waiting; initially, two aliens may arrive just a second away with

33% probability; then, arrivals will be completely at random; after

a given time, more than one shot might be required to kill aliens in

later levels (two shot s at l evel 2 , three shots at level 3, etc.); random

cool down periods between levels will increase anxiety and puzzle

players. Instructions: It is 1956 and you are the only p erso n left on

the face of the earth; you are in your bunker and watch the out side

world from your peep hole; the aliens are attacking and your only

chance is to kill them as soon as they are visible from your bunker

peephole.

Circle Wave. A circle appears and disappears at diﬀerent po si-

tions on a touch screen. The player must keep her ﬁnger on the

screen and must avoid the circle by moving his ﬁnger, without ever

lifting it from the screen. The circle slowly grows in size as the

game progresses. T he game ends when either the player lifts the

ﬁnger from the screen or it touches the circle. Resources: a white cir-

cle and a to uch screen. We could use two contrasting color s for the

circle and the background. Level Design: Initially, the circle grows

slowly, covering most of the screen in around three seconds and

it shrinks until it disappears in around two seco nds. As the game

continues, the circle grows faster and shrinks faster. Instructions:

Keep your ﬁnger o n the screen and avoid the white circle.

Constellation. Constellation is a memory game inspired by the

popu lar game "connect the dots". White dots appear on the screen.

When a dot is hovered (using a ﬁnger o n a touch screen or a mouse

pointer), another dot starts ﬂashing. When a dot it is no longer hov-

ered, it starts to fade out slowly. The last dot of the constellation

activates the ﬁrst dot of constellation. Players must hover all the

dots, following a predeﬁned sequence, as quickly as possible so

that when they reach t he last dot, all the constellation is blinking

at once. Resources: A display with two colors and an input system

(a touch screen or a mouse). Level Design: A constellation it’s a loop

of do t; level diﬃculty depends on the complexity of the shapes and

the t ime before hovered d ots disappear. T he faster dot that fades

out faster, deﬁne the minimum time required to complete the level.

The game should be a relaxed looping activity in which player

ﬁrstly discover the dot positions, then repeat the path to activate

the dots all together. Instructions: Hover near to the next ﬂashing

dot to complete the constellation. Dot-A-Mole. The player must

captures the d ots appearing on a touch screen before they turn oﬀ.

When players touches a dot a sound is played. Resources: a pixel

(or a shape); two colo rs for the shape and the background; a sound

to notify that the target has been hit; a touch screen. Level Design:

a level consists of a given number of pixels; initially, the rhythm is

slow and steady; as the game progresses, the rhythm increases and

might b ecome irregular while the time the pixel is active decreases;

in each level, players mu st capture an increasing percentage of pix-

els. Instructions: Catch as many pixels as you can.

Follow. A pixel moves on the screen in a pseudorandom way, mov-

ing away from the player’s mouse pointer. The player must try

to stay as close as possible to the pixel. Resources: a pixel and a

mouse. Level Design: player score is based on the d istance between

the mouse pointer and the pixel. As the score increases, the pixel

moves faster. A game lasts for around two minutes. Instructions:

stay as close as possible to the escaping p ixel.

Hop! The game is inspired to children jump rope games. Two iden-

tical squares are positioned at a short distance from each other.

One, the avatar, is still; the other one, the obstacle, rotates around

its center. Initially the avatar is positioned to the right of the ob-

stacle. Players controls the avatar square using a key. Every time

they hit the key, the avatar jumps in the direction determined by

angle of the nearest side of the obstacle. So for instance, if p lay-

ers hit the key when the obstacle is at 9 0 degrees, the avatar will

jump vertically since the nearest obstacle side is vertical; if play-

ers blink their eyes when the obstacle is rotate at 45 degrees, the

avatar w ill jump with a 45 degrees direction to the left or to the

right, depending on the obstacle position. The goal of the game

is to jump back and forth from one side to the other side of the

obstacle as many times as possible. When players hit the obstacle,

the game ends. Resources: Two squares, one for the obstacle, one

for t he avatar. A palette of two color s. One key. Level Design: Each

level lasts for ten full obstacle rotations. Initially, the obstacle ro-

tates very slowly and only in one direction. Rotatio n speed slightly

increases with the subsequent levels. Rotation direction might also

change during one level, later in the game. Instructions: Press the

key to jump the diamond as many times as you can.

I a m the Fastest! When the output system notiﬁes the beginning

of a match (for example, turning a pixel on or playing a sound),

two players take turns and have to press a key (or push a button)

as many times as possible before the output system notiﬁes the

end of the turn (turning the pixel oﬀ or playing another sound);

a player’s score is computed as the number of times the key was

pressed during the match, minus the times it was pressed outside

the turn (so that it is inconvenient for players to start pressing the

key before and after their turn) the match ended. The player with

the highest score wins. Resources: An input system (a button will do

the job) and an output system (a pixel that turns on, a played sound,

a momentary vibration). Level Design: There is no level design. In-

structions: Who is the fastest? Take turns with a friend. When light

is on, push the button as many times as you can before the light

turns oﬀ; be careful, pushing the button when the light is oﬀ will

result in a penalty. At the end, the light will ﬂash once, if the ﬁrst

player has won; twice if the second player has won; three times in

case of a tie.

Kick The Engine. All engineers know that to make things work

sometimes t he best solut io n to kick it. In this minimalist racing

game, players must beat their car engine to make it go fast and

overtake opponents. Bu t not too fast, otherwise players might lose

the control of the car and be forced to stop. The screen shows the

car position in the race using a line of 15 pixels (from ﬁrst to ﬁfth-

teen) and a 4x4 pixels grid that represents the distance of next op-

ponent to overtake and the ﬁnish line as a checkered ﬂag. Players

speed up by pressing a key (or tapping on an touch screen), the

One Pixel, One Interaction, One Game

speed decreases if players do not interact; players must keep an

adequate speed to overtake opponent while keeping the control

of the car. The grid gives players an indication of how fast they

should go to be able to overtake the opponent car: if the square

decreases in size, players should speed up; if the square increases

in size, players are getting near the opponent car and should b e

careful not too speed up to much and lose control of t he car. Re-

sources: 16 pixels to represent opponents and ﬁnish line; 15 pixels

to represent t he current car position in the race; 5 sound eﬀects

(two for the start, one for the engine sound whose pitch should in-

crease with speed, one when the p layer loses t he co ntrol of the car,

one for passing the ﬁnish line), an input system (a key or a touch

screen). Level Design: Diﬃculty depends on the opponent b ehavior

that should be controlled by basic heuristics (for example, the rub-

ber band). Instructions: Press the key (or tap) to increase speed, do

nothing to slow down; racing fast for prolonged periods make the

car uncontrollable and forces it to stop and restart the engine. “.-

.-.. .. ...- ." Players communicate with an astronaut (a non player-

character) on a damaged spaceship, lost in space. The astronaut

tries to contact someone using the only available mean of commu-

nication available, a binary signal, that is appears on the screen as

a single pixel which can be on or oﬀ. The player in an o perator

in a space station that has a Morse code table to decipher incom-

ing messages and a manual of the damaged spaceship with a map.

The astronaut sends messages that the player can replay if neede d.

The player reply u sing morse code by pressing a key. Like in well-

known text adventures, the player interact with the astronaut us-

ing basic verbs and composition of verbs and o bjects. The player

can cancel a message using another key. The astronauts also sends

short messages. The player wil l use the information in t he manual

to help the astronaut repair the ship to return to Earth. Resources:

A white pixel, a button to send Morse code, a rewind butt on to re-

play messages or cancel an outgoing message, and the manual of

the spaceship; sou nd eﬀects should be added t o improve engage-

ment and immersion. Level Design: This is a text adventure with

a minimal and cumbersome mean of communication. Commands

should be simpl iﬁed to ease communication using the shortening

used also in traditional text adventure in which "N" would corre-

spond to "Go North" and "O" would correspond to "Open". It should

be very short (b ecause of t he diﬃcult co mmunication interface)

and mainly focused on creating empathy with the lost astronaut.

Instructions: Help the astronaut come home. Listen to the Morse

messages arriving from the damaged spaceship and use the manual

to send instructions that will help the astronaut repair the damage

and come home safe.

Simpliﬁed Fruit Ninja. A pixel is falling from the top of the

screen. The player must click on the pixel before this reaches the

bottom of the screen. Resources: A falling pixel, a controller to click

the pixel (mouse, touch, pad). Level Design: In the ﬁrst l evel, just

one pix el appears at the top of the screen and it falls slowly. In the

next levels, the falling speed and the number of pixels increases;

additionally, there might be special pixels that players should not

select. Instru ctions: Click on the falling pixels, before they reach

the bottom.

Minimal W ipe Out. Players must collect a sequence of pixels that

fall down from the top of the screen toward the bo ttom. A pixel is

collected when it reaches the bottom of the screen inside a target

area, that is a small area in the middle delimited by using two pix-

els (one on the left and one on the right). The player can move all

the falling pixels on the screen at once, to t he left or to the right, in

order to make sure that the bottom one will fall into the t ar get area;

in addition she can also slow down the falling speed of the pixels.

At each moment of the game there w ill always be ﬁve falling pixels

on the screen, equally spaced on the y-axis of the screen, i.e., they

all fall with the same speed. As soon as a falling pixel is collected, it

disappears at the bottom of t he screen and a new one will appear

at the top. The game ends when one of the falling pixel reaches

the bottom of the screen outside the target area and thus it has

been lost. Resources: The game requires the presence of 5 pixels

that move from top to bottom and can be moved (all toghether) to

the right or to the left. The player actions will require three buttons:

one to move pixels to the right, one to move them to the left, and

one to slow down their falling. Finally, the target area at the bottom

of the screen shoul d be delimited using, at least, two ﬁxed pixels.

Level Desig n: The Level Design is based on the following variables:

(i) the initial speed of pix els, (ii) the changes over time of the falling

speed, and (iii) the relative positions of the sequence of pixels (that

appear will appear at the top of the screen). The game allows both

a procedural design of the levels or a d eterministic design. In the

latter case, players can exploit their memory (to memorize the po-

sition of the pixel sequences) to improve their performance; in this

case, it is also possible to use color to make the sequence of pixels

more easy to memorize. Instructions: Move the falling pixels on the

screen toward left or right using the arrow keys in o rder to collect

them inside the target area at the bottom of the screen. You can

also use the brake button to slow down the fall of the pixels. Try

to resists as long as you can without loosing any pixel! Minima list

Shooting Hoops. The game is a minimalist wrap of a basketball

shooting race. Players must keep a key pressed to load the shot

and release it when the pixel lights up to mark the basket. Players

must score as many points as possible in a given time to move to

the next level. The start is announced by a single sound; a sou nd

is played when players score; the end of the game is announced

by a sound repeated three times. Resources: one pixel that can be

on or oﬀ, one sound, one key or button to be pressed. L evel Design:

Level d iﬃculty is based on overall time available to the player, the

amount o f baskets needed to move to the next level, the amount o f

time before the pixel lights up. Instructions: a single sound marks

the start of the game; hold the key to charge t he shot and release

it when the pixel lights up to shoot hoops; score as many points

as possible b efore the time runs out; a cheering sound will accom-

pany every scored point; three repeated sounds mark the end of

the game.

One Voice. The player, represented as a circle, must dodge obsta-

cles and enemies using her voice. Squares represent obstacles while

diamonds represent enemies. The player can jump over enemies,

climb obstacles or sneak under them. Points are collecte d for jump-

ing over the enemies or sneaking under the obstacles. Resources:

Geometric shapes for circle, square, diamond; a microphone and

voice recognition software. Level Design: This is an endless run so

Lanzi and Loiacono, et al.

there is one level and diﬃculty increases over time. Initially, play-

ers will face an enemy and then an obstacles. Next, a se quence o f

enemies and obstacles will appear. Obstacles will form stairs that

player can cl imb to higher positions making it easier for the p layer

to jump over more enemies t hus collecting more points. Instruc-

tions: Just say "up", to start the game, climb obstacles, sneak below

them, and jump over enemies.

Overtake When the output system turn on, the headlights of a

car coming in the opposite direction; p layers have one second to

change lane by using the input system (by pressing a button or a

key); while holding the button, the players car will remain in the

overtaking lane; but they will have a split second to get back to the

main lane. Resources: An input system (a but ton, better if a steer-

ing wheel that presses the "button" when turns counterclockwise

over a certain point) and an output system (a pixel that turns on,

a sound, a vibrating system). Level Design: The frequency of in-

coming cars increases every t ime players complete a series of ten

overtakes. In stru ctions: You bet you can reach California by dawn;

go up on your ﬁreball and dart as fast as possible on the highway,

put yourself o n the overtaking lane to let the other car s eat dust;

enjoy the breeze but beware that you little to re-enter the main

lane.

Pixelcraft Together. This is a multiplayer experience in which

each player controls a pixel of a unique color within a persistent

world. Players move their pixels using either touch (or a mouse);

tap (or holding a mouse button) will draw a pixel on the world

background. The world is a huge canvas w here players can draw

copies of their pixels. Will players communicate? How will they

do it? What will they create? Will the world be come a random

collection o f pixels or will p layers try to self-organize to create

something meaningful? After a given number of actions have been

performed or a given time has passe d, the world is saved in a

gallery. Resources: Multiplayer support with online storage, many

colorful pixels, a controller (to uch or mouse). Level Design: There

is no playable level, players will create it together. A cool down

perio d between pixels’ creation should be introduced. Optionally,

obstacles and tr ails that players should follow coul d be introduc ed.

cooldown between t he creation of one’s own pixel and another. In -

structions: Tap to move, hol d to leave a footprint. Purgatory Player

move a w hite light (represented as a pixel) on a screen of 20x20

pixels, using a device equipped with accelerometers, and must cap -

tures b lue lights (blue pixels) while avoiding red lights. Resources:

sources of colored lights; a device with accelerometers. Level De-

sign: the ﬁrst level contains just a blue l ight (one blue pixel) and

a red one on a 20x20 pixels screen; the number of blue and red

lights increase in the subsequent levels making it more diﬃcult to

reach the blue lights. Instructions: you are an angel of purgatory

who must recover all the souls that have managed to ﬁnd peace;

move and tilt your device to the white light to recover all the blue

souls that are allowed t o reach the heavens; avoid al l the red sou ls

that are not yet ready to do so.

Quick Color. The screen displays a grid of pixels of diﬀerent color;

the grid colors change at ﬁxed time inter vals; the player must al-

ways select the only red pixel in the grid. Resources: a grid of col-

ored pixel, a target color, a pointer (touch or mouse). Level Design:

The ﬁrst level consists of a 4x4 grid; colors change every 5 seconds;

as the game progresses, the grid expands and the time intervals

between color change is reduced. Instru ctions: pick the red pixel

before colors change.

Quick Reﬂexes. Two symbols appear on-screen: one is a direc-

tional arrow, the o ther one represents either the concept of equal

or opposite. Players must press, within a certain time l imit, t he

same arrow if associated with the concept of equal, the opposite

one, otherwise. Players have a maximum number of mistakes they

can do in each level, for example, by pressing the wrong arrow

or no arrow at all. The game ends when that limit is reached. Re-

sources: six symbols, four representing the directions, two for t he

concept of equal or opposite; a controller with four direction (a

keyboard or a pad). Level Design: a level consists of a number of

conﬁgurations presented t o players; level diﬃculty is based on the

number of allowed errors, the time available to press the correct

arrow, and the time before the next conﬁguration appears. Instruc-

tions: Press the arrow in the same or opposite directio n depending

on whether the equale or o pposite concept is shown.

Ringtone Master. The game screen consists of ten pixels that can

be either black (when they are oﬀ), blue, or white (when they are

on). Each pixel corresponds to one of 0-9 digits of t he numeric pad.

Pixels tu rn on rhythmically, and pl ayers must press the correspond-

ing key on the numeric pad emitting a sound. Pixels will become

blue moments before turning white to give players t ime to prepare.

The series of sounds produced by following the rhythm imposed

by the pixels make up a song. Resources: ten pixels, ten sounds, and

a numeric keypad (keys 0-9). Leve l Design: a level is a sequence of

pixels that turns on following a given rhythm, allowing players

to play songs similar to those created with the composer software

of Nokia3310. Level diﬃculty depends on the rhythm complexity,

speed, and length of the melody. Instructions: Press the keys corre-

sponding to the pixels that turned white and keep the rhythm.

Rog. Players are adventurer that must sur vive a linear dungeon

they are exploring by ﬁghting the enemies they meet. T he game

ends when pl ayers reach the dungeo n exit. The current player view

of the linear dungeon is represented by a character displayed on

the screen. For example, an A might represent a doo r (the entrance

of the dungeon); an I may represent a snake to defeat. Players

might have an external legend to decipher the meaning of the char-

acters or simply learn by trial and error without any additional re-

source. Players have only one action (a key or a button to press).

Combat works as follows. P layers have only one stat istics, the en-

ergy, that works both as a measure of attack force and life points.

When players keep the key pressed, they consume energy, the longer

they keep the key pressed the higher the energy they consume.

Players’ energy is represented by an ASCII extended character,

with a value equal to the corresponding ASCII code (therefore be-

tween 0 and 255). The expended energy is shown o n-screen as it

is consumed. For every encounter, a random number is generated

(based on the type of enemy) and shown to the player. If the energy

that the player has invested in the attack is lower than the random

number, the enemy is defeated and the player can continue to the

next encounter. Otherwise, the player lo ses the invested energy

and must attack again. When the players energy falls below 32 (the

One Pixel, One Interaction, One Game

limit of visible ASCII characters), the adventurer dies. There might

be elements in the dungeon that help the player (for example, a

healing potion can restore energy). This combat mechanics recre-

ates the push-your-luck experience of rogue-like games, pushing

players to balance the amount of energy to invest in an attack, in

the most eﬃcient way possible, with a certain d ose of luck to con-

sider. Resources: one A SCII character on-screen for the encounter;

one for the energy invested in the attack; one for the current en-

ergy; one key. Level Design: It follows the typical structure of rogue-

like games presenting to players increasing powerful enemies and

new elements such as traps, potions, and o bstacles. In stru ctions:

Escape from the Dungeon; push the button to proceed; hold the

button down to decide how much energy to use to attack enemies.

If the energy expense is greater than the enemy at tack, the enemy

is defeated. If your energy drops to " ", you lost.

Role Pixel Game. In this minimalist role playing game, four pix-

els on the screen show the character’s equipment (gray if common,

blue if epic, orange if legendary, with associated a health value,

damage, and percentage of increasing dodging), the health of the

character (green, yellow, or red), the presence and level of the mon-

ster in the room (using the color coding used for the equipment),

and ﬁnally the presence and type of treasure in the room (equ ip-

ment or health potion Indicated by red color) or exit (white). Play-

ers can move to another room (using the four arrows to move in

the corresponding cardinal direction), collect a treasures and po-

tions, or attack. Players’ score is based on the number of explored

rooms, enemy killed, treasures, and equipment collected. Resources:

four pixels and seven sounds for the steps or door that closes at

the entrance in a room; the player’s successful at tack and dodging;

the damage received successful attack; collecting the room content,

and victory. One input to hit and collect , four cardinal directions

(arrows on a keyboard or swipe on a touch screen). Level D esign:

The diﬃculty increases with an increasing number of enemy en-

counters, fewer potions, and a greater number of mandatory ﬁghts.

Instructions: Explore the dungeon moving in the four cardinal di-

rections to enter new rooms; press a key to attack and collect dun-

geon treasures, make sure you improve your equipment to face

increasingly strong enemies and get healthy and except for exit.

See(D) Me Grow. Player plant a seed (a brown pixel) touching the

screen. The seed blossoms over time (indicatively in half the pix el

beco mes green), the longer the time the player spend watching

the plant grows, the higher the probability that a rare ﬂower will

bloo m (represented as a rare pixel color). Resources: a pixel, two

sounds (one for planting, one for blooming), a touch screen. Level

Design: Levels might involve increasing interaction wit h t he seed

to make it bloom or to avoid w it hering. Instructions: Tap the screen

to plant a seed, tap again to collect the blossomed ﬂowers.

Talking Robot. At the beginning, the computer emits a series of

sounds representing all the letters of the alphabet in sequence from

A to Z. Players must ﬁnd a way to annotate the mapping between

letters and sounds. Next, the computer emits a series of complete

sentences, using the same sound-based coding like a sort of R2-

D2. Players must decipher the sentences and annotate the sol ution

(on a piece of paper or a notebook). Finally, the computer show

the solution (it could pr int it on screen or play it as audio) and

players must chec k how well t hey de ciphered t he messages. There

is no explicit score but just the players self evaluation of their own

performance. Resources: there is not input just audio output; paper

and pencil for the taking notes; a way to show the solution which

could be player using the same audio or printed on screen. Level

Design: the game starts with very short sentences that can increase

in length when p layers move to the next level; reproduction speed

might increase and the number of the sentence repetitions played

may dec rease to increase the diﬃcul ty. Instructions: Listen to the

26 sounds representing the letters of the alphabet from A t o Z and

ﬁnd a way to remember what sound is associated to each letter;

next, a sentence will be played several times; decipher it before it

stops being repeated.

The Key A sequence of letters appears on screen, one at a t ime,

and players must press the correct key as quickly as possible. Re-

sources: a device with a keyboard to enter all the letters from A to Z

and the digits from 0 to 9 (a computer or a mobile device with a soft-

ware keyboard). Level Design: a l evel consists of a sequence of ten

symbols. The ﬁrst l evel asks pl ayers to press the key correspond-

ing to the same symbol appearing on the screen. In the following

levels, players may be aske d to p ress the next or previous symbols

of the one appearing on screen; the time available to press the key

might also be reduced. Instructions: press the same symbol for the

ﬁrst level, and press the following/preceding symbol for the next

ones.

They Never Stop. Players shoot advancing enemy pixels they are

advancing. Enemies change their state periodically switching be-

tween an invincible state, a normal state and a b rief vulnerable

state. Bullets recharge slowly and there are at most t hree live bul-

lets at once. Thus, players must carefully decide when to shoot en-

emies to hit them in their vul nerable state and not wasting b ullets

when they are invincible. Resources: two pixels for player and the

enemy, four colors, a key to press (or butt on). Sound and music to

make it a complete rhythm game. Level Design: one level lasts for

around two minutes and the speed of enemies and their spawn rate

increases when players step to the next level. Instructions: Press the

key to shoot the enemies when they are most vulnerable; do not

waste bullets on invincible enemies.

To Be Or Dot To Be. The game is a minimalist interpretation of

the classic Frogger. A pixel is positioned at the lower edge of the

screen. Players use a key to make the dot move of a ﬁxed amount.

In t he middl e of the screen there is a row of 5 dots that moves hori-

zontally: ﬁrst from left to right and then from right to left. Players

have to guide their pixel to the other side of the screen by crossing

the line of moving pixels, without hitting the moving pixels. Re-

sources: A pixel to use as the player character and for the moving

line of pixels; two colors, one for the background and one for the

dots; a key. Level Design: Each level requires players to guide ﬁve

pixels across t he screen. Initially, line of pixels moves slowly at a

constant pace. Every time a pixel crosses the screen it is added to

the moving line, becoming an obstacle for the next dot. So the sec-

ond level will contain two lines of ﬁve dots each, the initial ones

with the pixels that crossed in the ﬁrst level. The two lines move in

oppo site directions. Instructions: Bring the pixels across the screen

without hitting the moving lines.

Lanzi and Loiacono, et al.

7 DISCUSSION

The game designs we included in the previous section provide a

good overview of the variety of themes and mechanics of the con-

cepts we received. There are games that are purely reactive (e.g.,

Dot-A-Mole and Quick Reﬂexes), involve chasing (e.g., Follow), idle/waiting

(e.g., See(D) Me Grow), memory (e.g., Constellation), quick reaction

(e.g., The Key, Quick Color, and Quick Reﬂexes), experiential (e.g.,

Pixelcraft Together), and multiplayer (e.g., I am the Fastest! and Pix-

elcraft Together). Some mechanics are well-know (e.g., One Voice

has a rather typical mechanics with an experimental voice-based

control); some are the same use d in C64 and Apple II games (I Am

Fastest has the same mechanics of race track events on old Olympic

video games). The combat mechanic of Rog recreates the push-

your-luck used in several tabletop games. Hop! is inspired to the

children jump rope games. Several games are based on the play-

ers’ memory (e.g., Talking Robots, Constellation), others requires

planning abilities (e.g., 3.. 2.. 1.. Go! and Kick the Engine), most of

the are purely reactive. Note however that, some reactive games

can be made memor y-based through level design. For example, Cir-

cle Wave could become memory based by making the sequ ence of

circle waves deterministic which would be equivalent to asking

players to learn the waves’ behavior (similarly to what is done in

Constellation). There is also a wide variety of genres. There are rac-

ing games (e.g., Minimal Wipe Out, Overtake, and Kick The Engin e),

rhythm games (e.g., Ringtone Master and ), platformers (e.g., One

Voice), role-playing games (e.g., Rog and Role Pixel Game), casual

games (e.g., Minimal Fruit Ninja), adaptation of arcade games (e.g.,

They Never Stop and To Be Or Dot To Be), and experimental (e.g.,

Talking Robot). Some games are completely abstract (e.g., Hop!, Fol-

low and Constellation), others are grounded in speciﬁc themes. It

is interesting to note that, in terms o f score system, most are win-

loss games that challenge the player to complete as many level as

possible, so me have a scoring system, while others are compl etely

experiential (e.g., Pixel With Friends and See( D) Me Grow).

If we analyze them using four criteria considered in [18] (sys-

tem, control, visual, aural ), we note that all games have minimalist

systems with a very limited set of choices that may enable purely

reactive behavior as well as planning (e.g., 3.. 2.. 1.. Go!) or deep

gameplay using additional material in “.- .-.. .. ...- ."). At control level,

there is a neat distinction between games using keys or buttons

and those nee ding a touch interface (which can in some cases re-

placed by a mouse p ointer). Ten years ago, when minimalist game

design movement started to get momentum [18], touch interfaces

were in their infancy and several minimalist games were initially

design for the keyboard and then upgraded t o touch [5, 24]. Today,

touch interface has become a commodity and thus several design-

ers view it as minimalist. If we cross data of designers’ age and

the use of touch interface, we note that older designer tended to

stick to the key and button approach whereas the touch interface

was suggested mainly by younger designers.

Visually, all games

are c ompletely abstract. In aural terms, designers have used sound

eﬀects to reinforce the narrative (e.g., Kick the Eng ine and Mini-

malist Shooting Hoops); most designers used sounds for providing

We chose to leave the concepts anonymous and not to include any data about the

age or other characteristics of the designers to avoid any sort of bias in the reader and

for obvious privacy reasons.

feedback while others made sound the main subject of the game

(e.g., Talking Robot).

The concepts highlight the important role of narrative even in

minimalist games. Two games, Aliens Attack from Deep Space and

Minimalist Shooting Hoops, at the system level, are identical to the

basic example games that were given in the invitation we sent to

designers. The former asks the player to shoot the alien as soon

as it becomes visible through the peephole (which is identical to

the basic example game in Section 6); the latter asks the player to

charge the shot b y keeping the key pressed until the pixel turns

on (which the same game with inverted control discussed in Sec-

tion 6). However, the narratives that the designers have created

around the same mechanics make the games feel completely dif-

ferent. Narrative is also used to create depth in a game wit h a cum-

bersome communication interface like “.- .-.. .. ...- ." in which the

use of a p rinted manual may make it less minimalist but, at the

same time, increase complexity, immersion, and depth.

8 CONCLUSIONS

We presented an experiment on minimalist game design. We started

from an example of the most straightforward game we could de-

sign (involving just one p ixel and one interaction). We sent ou r

minimalist game to students and professional game designers and

challenged them to create original games using the least amount

of visuals and user interaction. We did not impose any constraints;

we just provided our simple game as inspiration. We received more

than 1 20 game concepts and presented some of them in this paper

discussing the vision of Minimalist Game Design [18] t hat tran-

spire from the concepts, ten years after the seminal paper by Nealen

et al. [18] started the discourse on minimalism. We performed sev-

eral analysis on the design documents we received to search for

patterns and semantic structures. We applied a wide variety of well-

known text mining techniques including word embeddings, topic

modeling, and text clu stering [2, 7, 9, 10]. However, our analyses

did not revealed interesting patterns; our results suggest that this

is probably due to the relatively small number of concepts and the

conciseness of the descriptions. We believe our experiment can be

an interesting tool for teaching the essence of game design to stu-

dents. Accordingly, we plan to propose the challenge again next

semester to the incoming game design students. We consider this

an ongoing experiment and we hope t hat increasing the amount

of concepts will enable us to do more advanced analysis on the

design documents in the future. We also welcome submissions of

new minimalist design concepts from anyone interested in partic-

ipating using the form at https://forms.gle/uPk1aWkx9Gr9kVgk9.

REFERENCES

[1] Mike Bithell. 2010. Thomas Was Alone. Retrieved March 5, 2022 from

http://www.thomaswasalone.com/thomaswasalone/

[2] Piotr Bojanowski, Edouard Grave, Armand Joulin, and Tomas Mikolov.

2016. Enriching Word Vectors with Subword Information. arXiv preprint

arXiv:1607.04606 (2016).

[3] Jeppe Carlsen. 2013. 140. Retrieved March 5, 2022 from

https://carlsengames.com/games/140/

[4] Ter ry Cavanagh. 2012. Super Hexagon. Retrieved March 5, 2022 from

https://superhexagon.com

[5] FlukeD ude. 2009. The Impossible Game. Retrieved March 5, 2022 from

https://impossible.game

[6] Ojiro "Moppin" Fumoto. 2015. Downwell. Retrieved March 5, 2022 from

https://downwellgame.com

One Pixel, One Interaction, One Game

[7] Maarten Grootendorst. 2020. BERTopic: Leveraging BERT and c-TF-IDF to create

easily interpretable topics. https://doi.org/10.5281/zenodo.4381785

[8] Aaron Isaksen, Daniel Gopstein, Julian Togelius, and Andy Nealen. 2018.

Exploring Game Space of Minimal Action Games via Parameter Tun-

ing and Survival Analysis. IEEE Trans. Games 10, 2 (2018), 182–194.

https://doi.org/10.1109/TCIAIG.2017.2750181

[9] Armand Joulin, Edouard Grave, Piotr Bojanowski, Matthijs Douze, Hérve Jégou,

and Tomas Mikolov. 2016. FastText.zip: Compressing text classiﬁ cation models.

arXiv preprint arXiv:1612.03651 (2016).

[10] Armand Joulin, Edouard Grave, Piotr Bojanowski, and Tomas Mikolov. 2016. Bag

of Tricks for Eﬃcient Text Classiﬁcation. arXiv preprint arXiv:1607.01759 (2016).

[11] Jesper Juu l. 2003. The game, the player, the world: looking

for a heart of gameness. In Digital Games Research Conference

2003, 4-6 November 2003, University of Utrecht, The Netherlands.

http://www.digra.org/digital-library /publications/the-game-the-player-the-world-looking-for-a-heart-of-gameness/

[12] Jesper Juul. 2007. A Certain Level of Abstraction. In Proceedings of the 20 07

DiGRA International Conference: Situated Play, DiGRA 2007, Tokyo, Japan,

September 24-28, 2007, Akira Bab a (Ed.). Digital Games Resear ch Association.

http://www.digra.org/digital-library /publications/a-certain-level-of-abstraction/

[13] Marie Kondo. 2014. The Life-Changing Magic of Tidying: A simple, eﬀective way

to banish clutter forever. Ten Speed Press .

[14] Korokomi Collective. 2010. Gamma Announces ’One Button’

Theme For GDC 2010 Showcase. Retrieved March 5, 2022 from

https://www.gdconf.com/news/gamma_announces_one_button_the

[15] Michael Lankes. 2020. Social Gaz e in Minimalist G ames. In CHI PLAY

’20: The Annual Symposium on Computer-Human Interaction in Play, Vir-

tual Event, Canada, November 2-4, 2020, Pejman Mirza-Babaei, Victoria

McArthur, Vero Vanden Abeele, and Ma x Birk (Eds.). ACM, 450–460.

https://doi.org/10.1145/3410404.3414265

[16] Nick Montfort and Ian Bogost. 2009. Racing the Beam: The Atari Video Computer

System. MIT Press, C ambridge MA.

[17] David Myers. 2009. In search of a minimalist game. In Pr o ceed-

ings of the 20 09 DiGRA International Conference: Breaking New

Ground: Innovation in Games, Play, Practice and Theory, DiGRA

2009, London, UK, September 1-4, 2009, Tanya Krzywinska, Helen W.

Kennedy, and Barry Atkins (Eds.). Digital Games Research Association.

http://www.digra.org/digital-library /publications/in-search-of-a-minimalist-game/

[18] Andrew Nealen, Adam Saltsma n, and Eddy Boxerman. 2011. Towards minimalist

game design. In Foundations of Digital Games, FDG’11, Bordeaux, France, June 28

- July 1, 2011, Marc Cavazza, Katherine Isbister, and Charles Rich (Eds.). ACM,

38–45. https://doi.org/10.1145/2159365.2159371

[19] Dong Nguyen. 2013. Flappy Bird. Retrieved March 5, 2022 from

http://ﬂappybird.io

[20] Jack Oatley and Gurpreet Singh Matharoo. 2020. LOWREZJAM 2020. Retrieved

March 5, 2022 from https://itch.io/jam/lowrezjam-2020

[21] Warleson Oliveira. 2020. UNO Minimalista. Retrieved Ma rch 5,

2022 from https://shop.mattel.com/products/uno-minimalista-gyh69

https://www.instagram.com/p/B89TWTdlEXf/.

[22] RAC7 Games. 2015. Dark Echo Game. Retrieved March 5, 2022 from

https://www.darkechogame.com

[23] retroshark and 7Soul. 2020. GBJAM 8. Retrieved March 5, 2022 from

https://itch.io/jam/gbjam-8

[24] Adam Saltsman. 2009. Canabalt. Retrieved Marc h 5, 2022 from

http://www.c anabalt.com

[25] Santa Ragione. 2011. Fotonica. Retrieved March 5, 2022 from

https://www.fotonica-game.com

[26] Dan Troyka. 2000. Breakthrough (Winner of the 2001 8x8 Game Design

Competition with the simplest ruleset). Retrieved March 5, 2022 from

https://en.wikipedia.org/wiki/Break through_(b oard_game)

[27] Wikipedia contributors. 1992. UNO Card Game — Wikipedia,

The Free Encyclopedia. Retrieved March 5, 2022 from

https://en.wikipedia.org/wiki/Uno_(card_game)

[28] Wikipedia contributors. 2021. List of Abstract Strat-

egy Games — Wikipedia, The Free Encyclopedia.

https://en.wikipedia.org/wiki/List_of_abstract_strategy_games [Online;

accessed 28-May-2021].