@FishW Hmmm im assuming you used like pistons with the hay bales thing, and then the top has dispensers but that leaves a few unanswered questions.
Another option is that you somehow get into a bedrock hole and trap them.

Sorry for going off topic, but this brings up a question: @Nysic @Blackened_Dawn (because I think these admins are active on the forums) Are we allowed to make holes in the overworld that go into the void?

Hmm, I'm almost positive it involves entities in walls. Does it? (I've got to go for about two hours after this post, so I probably won't read your reply until then.)