So I was wandering if letting zombies naturally funnel and gather to a villager before killing them counts as an advantage. Keeping the villager safe is the only thing that would be penned in so to speak. Zombies would be allowed to roam free.
I would imagine that it's the exact manner that you contain and kill them that would cause the issue. So long as it's a fair fight, I think it would be fine.
They would migrate to the villager under their own power and in theory roam around in say a 20x20 room
I think that it would count as an arena if there was no bait, such as the villager. NikleKing's mob arena has no bait for mobs, they spawn naturally. I'm not too sure. But I still think that it would be a bit unfair because it's just a quick way to get xp.
One could argue that these mobs also spawn naturally; having bait is like having a theoretical wall to the arena, both prevent mobs from moving too far away. The villager to me is like a snow golem with aoe, all it does is draw them in, and serves no other purpose.
I can see where you're coming from as well. Well, Moose clarified it, so long as no advantage is given, then it's fine.