Two pixels are better than one. In local co-op mode, you and a friend can both collect enemy pixels independently. When one of you dies, the other can revive you simply by touching your pixel.
In this non-shooting shoot 'em up, you are a single white pixel who can absorb the bodies, abilities, and weapons of every enemy pixel you collect. It's up to you to stay either a small and nimble ship, or turn large and powerful. Just remember: protect your core white pixel, because every mistake could be your last.