here's an idea: quads game where each player has a special ability. Is it ballanced? no idea but sounds fun.
red/pink: the muscle. receives +1 troop to drop every round. the special attack force!
green/teal: the wheelman. Can perform 2 forts at the end of his turn! (note that unlimited forts can't be applied to this game mode)
blue/orange: the doc. receives 1 extra troop at the end of his turn that he can place anywhere on the team (like a deferred troop)
yellow/grey: the brain. If he holds a region but one held by a teammate, he doesn't need to teamkill to get the region bonus. (example, if yellow has lima, sao paolo bogota and blue has buenos aires, yellow has the SA bonus)