A Multiplayer game?

I have the basic actions finished for my player, and now need to make it all work for a second player. I want to at least have a local multiplayer mode. I would really like to have online multiplayer as well, but we will see. My aim is three characters, and 3 or 4 different stages.

 

The game idea is to make a 2D fighting game…with unconventional weapons…  Right now one green colored square bashes on the other unmoving  one.