how do you play co-op?

[default_loser]

I've only played this game a little bit, but I can't figure out exactly how you play co-op. The options menu only mentions Player 1, giving me the choice between Keys/Mouse and my XBox360 controller, but says nothing about other players' input. I would have thought it would let one player use Keys/Mouse and another use the controller, but even if I plug in an extra controller, I don't see an option for co-op anywhere.

Is co-op one of the game modes you have to unlock? I only have 4 modes unlocked right now, so maybe that's it?

[tOoOm]

If you're playing with a keyboard as Player 1, Press A (or 1 in my case) on your controller at the main screen. That part works for me.