Mars 21

Cooperative 2D platformer

Download the game:
PlatformPC (Windows, OS X, Linux, WebGL)
Mode2 players co-op
Target audience3-11 years old
Play time4 minutes
TechnologyUnity 5
Team4 people
Production time1 month (+2 months polish)
RoleGame design, Gameplay programming

Mars 21 banner full

Playing instructions

We recommend to play the game at 720p minimum.

The WebGL version does not feature the opening movie.


You can play with two gamepads or with the keyboard. Gamepad is not supported in the WebGL version.

  • Menu

    Keyboard Gamepad
    Navigate Arrow keys Stick / D-pad
    Confirm ENTER A button

    In-game system

    Keyboard Gamepad
    Exit level ESCAPE
  • Astronaut

    Keyboard Gamepad
    Move Left & right arrow keys Stick / D-pad (Horizontal)
    Climb ladder Up & down arrow keys Stick / D-pad (Vertical)
    Jump SPACE A button
    Interact B key X button


    Keyboard Gamepad
    Move WASD (ZQSD on Azerty) Stick / D-pad (A button also moves up)
    Interact E key X button


Keyboard Gamepad
Warp alien to astronaut U key
Restart level  I key
Warp to previous/next checkpoint O/P key


Mars 21 is a cooperative platform game for 2 players on PC. Player 1 controls an astronaut moving on the ground and player 2 controls a flying Martian creature. The two characters have different abilities and the players must cooperate to finish the game.

alien picture



The game was developed in 1 month as our first video game project at Gobelins. The setting of the game is loosely based on science fiction short story collection The Martian Chronicles by Ray Bradbury. The game was further polished over 2 months in parallel with the development of new projects.


  • Long Nguyen Huu: Game design, Level design, Gameplay / UI programming
  • Ludovic Marguerie: Game design, Level design, 3D modeling, Story, Sound design
  • Coralie Perot: Concept art, Character design, Story, Opening movie
  • Jean-François Cœur: Graphics programming, Gameplay / UI programming


Game design

  • Astronaut control design
  • Alien damage rules

Level design

  • Setup of environment colliders
  • Fine platform and hazard placement
  • Checkpoint placement
  • Light cues

Gameplay programming

  • Astronaut character controller
  • Damage, death and respawn system with checkpoints

UI programming

  • UI tween animations
  • UI and movie subtitles localization system


  • WebGL support
  • Various optimizations

3D integration

  • Integration of humanoid model and animations
  • Damage particle effects


  • English translation (from French)

Unity packages


  • Setting based on The Martian Chronicles by Ray Bradbury (especially The Green Morning and The Watchers)
  • Electric Sparks SFX by Connum on freesound (CC-BY-NC 3.0)