They should make it a tag team game that controls like the first Powerstone, so you have 4 people on the screen at once (or hell, maybe more), and 1 person can only fight 1 other person the entire time, but they can still get affected by the other fighters (ie 1 guy could throw a bomb at his enemy fighter, the bomb explodes and can still damage the other fighters in the area).
Powerstone 2 was fun, but it was all over the place, almost closer to a Mario Party game than a fighting game.