What I think would be really cool would be a plugin that allows the players to make groups of mobs that would fight eachother, for an arena type thing. My best idea for defining what mobs are attacked by which is that they could look for mobs with a certain name, like a group of mobs named ArmyA would attack a group of mobs named ArmyB if they came within their line of sight. This is something I really want in my server, and it would mean a lot if someone could make this a reality.