Nether portal obsidian farm

Mag Plum's fourth revision of the nether portal obsidian farm, and the current answer for recent versions. Withers held under a portal array destroy the portal blocks, snow golems relight them, and the game regenerates the obsidian instantly. It uses no duping of any kind, which is why it still works on 26.2 where most obsidian farms have been patched out. The whole build hinges on portal linking, so where you put it matters more than how you build it.

• Portal placement is the whole problem. Build high, away from caves, and seal or flood anything below, or the portal generates somewhere other than the farm and nothing happens at all.
• Break the portal that gets created when you first enter the Nether. If you leave it, it can link to an overworld portal and steal the farm's connection.
• Keep the nether side at the same height as the overworld part, otherwise the portal generates far below where it should.
• In snowy biomes the water freezes. Put slabs in the water or roof it over the way the updated schematic does.
• On servers a TPS drop breaks it. Portals start generating in other spots, one eventually appears inside the chamber and pushes the withers out.
• The shulker box loader is optional. About 24 hoppers from the chests to the hopper under the cake does the same job without the shells, observers, dispensers and pistons.