Need mobs to fight? Maybe you need some experience or item drops? Or you just want to work on your MCMMO skills.
Try out /warp Cash4Mobs
Here you can be left alone to fight whatever mobs you like. Or bring a friend to help you out.
Looking for some entertainment? Maybe you want to fight a ton of mobs just for the challenge. Want to spawn mobs and watch other people fight them? Spawn a ton and watch them suffer!
Try out /warp MobArena
Here you are put in an open space fighting alongside whoever wants to fight with you. Hopefully someone too sadistic doesn't come through and summon 100 blazes for you to fight...that wouldn't be very nice...