Portal 2 is a 2011 first-person shooter/action/puzzle game developed by Valve Software and the sequel to the 2007 game, Portal. The game has received two cross-promotions with the BIT.TRIP series. In the Steam version of BEAT, a fourth stage, titled <TEST>, was made available for a promotional event called the Potato Sack, wherein players would seek out potatoes hidden in various Steam games for a chance to play Portal 2 early. In the Steam version of Runner2, Atlas, a character from Portal 2's co-op campaign, is included on the Good Friends DLC pack as one of the additional playable characters. He is exclusive to the Steam release and is the only exclusive character across any version of the game.