Multiplayer.
Transformice is a multiplayer game, where you are a small mouse out to get a cheese and bring the cheese back to the hole.
The game includes a physics engine, so interactions between players are realistic.
Each round lasts 2 minutes max, and in order to help the 20 or so mice-players to get the cheese, a player will be chosen to be the powerful shaman and will be able to spawn different objects to guide the mice.