Player manipulates blood cell trying to transport as much oxygen to heart as possible. To do it player has to avoid collisions with obstacles and enemies.
Backwards: One or more aspects of the game works the opposite as would normally be expected: maybe the controller is reversed (left is right, right is left), maybe you win lives every time you die, maybe it scrolls to the left and your character moonwalks.
No cheating (please): The game system relies on willing player participation to enforce the rules of the game world (e.g., hold your breath, close your eyes, etc.).
Approved for All Audiences: The game must not show any violence, not even cartoonish. Stepping on living mushrooms is off the list, as is killing any type of enemies, not even undead, though we know they’re already dead…