You gotta kill your friend, but you can't retrace your steps because I programmed it that way.
Blue: WASD to move, left shift to shoot
Red: Arrows to move, right shift to shoot
This is some kind of inspired mashup of the can't-retrace-your-step puzzle and arena shooting duels. It adds an extra level of strategy of conservative play that I really like.
Some day, I'll sit down with a friend and make him or her play all the two-player Glorious Trainwrecks games with me.
Also, seriously, fuck stickykeys.