The inner surface is constructed at the ideal mob spawning distance from the player who stands in the middle. All the mobs can move, none can despawn, and they can't see the player. The lower half is cyclically flushed by a ring of dispensers wired to a piston clock. The mobs are collected and killed, and the items are delivered to the player via an automatic item elevator--even the xp orbs if you want to do some archery practice.
I might improve it with shelves of spawning pads in the upper hemisphere, also built in the mob sweet spots.
I'll probably build this next in survival on my server. Most likely I'll get up to it via a nether portal.
At present, Monkeypuzzle has 426,304 views spread across 308 videos for Minecraft, with the game making up over 7 days of published video on his channel. This makes up 3.76% of Minecraft content that Monkeypuzzle has uploaded to YouTube.
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