Vikings On Trampolines is an upcoming game by D-Pad Studios, the same team behind the neat-looking Owlboy. It's about... Vikings on trampolines. You control one Viking, somebody else controls the other, and you have to bounce around trying to not touch the ground, or you will die a horrible, horrible death.
Simple, then, like many of the best multiplayer combat titles are. It'll be out on PC after Owlboy is done, and if you're wondering, that should be pretty soon (fingers crossed!).