Instant portal obsidian farm

WMC's own design, and the first obsidian farm that never touches the End. Withers held in the overworld are aimed at villagers so their skulls keep destroying a nether portal, which the game regenerates instantly, and a tripwire hook duper feeds the whole thing. Leaving the end platform free is the point, because on a server that platform is usually somebody's enderman farm. It is also the most dangerous farm in the library, with builders reporting escaped withers wrecking large parts of their world.

• Spawn proof everything below the platform. Portals generate in caves underneath, sometimes ninety blocks down, and this is the most common reason the farm does nothing at all. Flood them or slab them out.
• Roof the villagers over. In a thunderstorm lightning converts them to witches, the withers lose their target and escape.
• The material list in the video is incomplete. The tripwire hook duper parts, temporary blocks, extra slabs, soul sand and the ender pearl are all missing from it.
• Orientation matters and is barely explained. The duper's dropper faces north with the hopper line east, withers face north and villagers south.
• If the tripwire hook duper stops working on newer versions, build a carpet duper instead and feed the dropper through hoppers powered by two observers.
• Put a hopper minecart under the platform. Broken obsidian landing on the intact portal base is otherwise left behind, and about half the output ends up teleporting into the nether.