Not content to give us fresh puzzles, more chill-inducing GLaDOS dialogue, and a new character voiced by a British comedian, Valve has built a co-op mode into Portal 2. The teaser video below, originally posted by GameTrailers.com, provides a glimpse at the new game mode:
Predictably, the female protagonist doesn't make an appearance here, having been replaced by a pair of mischievous-looking robots... with portal guns, of course.
I wouldn't be surprised if Valve included some special maps with puzzles tailored for co-op. Otherwise, a second player might feel like a bit of a third wheel. At this point, though, Valve doesn't seem to have announced any specifics about Portal 2 co-op—like how many players will be supported, for instance.