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.)

@TheSpiderman2013 Spill the beans...
I've got no clue.

No wait! D: I'll keep asking for hints.

Does it have to do with entity collisions?

Does it involve any pistons whatsoever...?

Here's an example. Notice there is no avatar for this post.

EDIT: Was this fixed this quickly?

I noticed that on the forums, if you make a post directly after another one, your avatar will only show up on the first post (this is pretty neat). However, if the first post is deleted (for moderation or other reasons), the avatar disappears. I think the avatar should move down to the second post instead of being removed when the first post is deleted.

I was going to post a screenshot of a skeleton horse in the ocean at the world border, but it despawned before I could get there. :(

@Nysic @Triatomic you won't be able to as that would require breaking bedrock which requires creative mode.

@NutjobBob No, see this thread:
link

@Nysic it doesn't require creative mode, but @NutjobBob thank you for clarifying with that post. I read Crafty's response and he doesn't allow breaking bedrock.

@NutjobBob This can be easily prevented by removing all valid tp spaces around the trap

That's a lot of work to make an 8x8x8 cube, but I supposed good traps need hard work. I'll keep thinking.

@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?

with a plushy armadillo

@NutjobBob I think I have created the best possible tpa trap. It puts the player in a 2x2 space where they are unable to break or place blocks. Arrows or harming potions can be fired into the space, and lava can be added at head height for extra fun. I believe that other than tping out or getting another player to dismantle the trap, there is no way out, even with ender pearls.

I wonder if anyone can figure out how I did it.

Haha I thought of a funny way to do this. Fill the trap with tons of zombies or something (spiders would fit nicely) so that the player doesn't have any room to mine out.

Or did you use some piston based contraption which pushes them so they can't mine...?