Biplayer matches
It's like singleplayer, but only 2 people. You're fighting your opponent's ghost, and you can R and E as much as you want, because there is no collision. There are shift frames and that type of stuff you can do in Singleplayer. Or, a timed match where your enemy can space and progress faster than your enemy. A game of who knows their joints better?
I like the Biplayer idea because it would be a GREAT way for parkouring, sparring, tricking, and collabing.