Region the Spawning

Hello all,
Ok so I'm wondering if it's possible to deny the mob spawning in certain regions (Denying Egg use in certain worlds). Ok so my plan is to have an arena in a separate world on my Skyblock server, where in that world, only those Mythical Mobs spawn eggs will work. I was also wondering if there is a way for you to kill off that mob once everyone leaves that world basically declaring the Mythical Mob as the Champion

Kind Regards,
BoostedNetwork