Nether roof portal magma cream farm

A magma cream farm on the nether roof above a basalt delta. Magma cubes spawn on the farm and pass straight through its 132 nether portals to one overworld portal, where wither roses kill them and a loader packs the cream into shulker boxes. You AFK in the nether above the farm, and the cubes going through keep the overworld side loaded. It suits a player who has obsidian in bulk and needs magma blocks, for a gold farm for example. The overworld portal has to sit at the nether farm's centre coordinates times 8, or many cubes stay in the nether. The video is a short showcase, so the build comes from the world download.

• Centre the overworld portal on the nether farm's centre x and z times 8, and remove any generated portal near it. A portal 5 blocks off leaves cubes behind. Several builders hit this.
• Light every portal on both sides, then walk through once from the nether side. The portals do not link until someone does, and no cube passes. Creator's reply.
• In the world download run /gamerule doMobSpawning true first, it was saved with mob spawning off. Creator's FAQ, after many builders saw no spawns.
• Check the shulker box loader before you AFK, several builders found boxes not loading. One fix with 3 likes: place a block behind the two observers in the iron trapdoor column.
• On a server keep an account AFK on the overworld side. When another player is in the overworld, cubes that arrive outside that player's range despawn. Creator's reply.
• Add layers only upwards, with more loaders for the extra cream. Widening the farm stops the portals linking to one overworld portal. Creator's FAQ.