Cooperative
Cooperative is a gameplay mode that is nearly the same as single player, except multiple players can work together. There is one main change in Coop gameplay which is players can use each other as springs of sorts by jumping on one player’s head, and then have the other player jump. This mode can only be used on a split screen game – however, using several fan-made programs or the command line, it’s possible to play Cooperative over the internet.
Playing Cooperative Online
Cooperative can be played over the internet, but nobody can hurt or die except for the host of the server. Programs like xJJ2 can aid in hosting online cooperative servers. Starting a cooperative server using the command line is also possible. Playing this game type online may be useful in that single player levels can be tested by a few people at once.