Armadillo infestation wither rose farm

An infestation wither rose farm where the wither never enters the Overworld. The wither is trapped in the Nether targeting an iron golem, but its skulls travel through a nether portal and come out in the Overworld, where they kill silverfish and drop wither roses. The silverfish come from armadillos dosed with a splash potion of Infestation and held over a campfire, so every tick of damage spawns more. Smooth stone slabs take the blast because blue skulls can destroy almost anything, including obsidian, and a soul sand bubble column with water handles the rest. Nothing dangerous is ever on the Overworld side, which is the whole point of the design. Around 780 wither roses per potion.

Make the bubble column three blocks tall rather than two. Nightstick24 says that alone stops the Overworld side blowing itself up, and jblader111 and Nanoue42 both needed it on 1.21.11 along with a nether portal one block taller.
Never substitute plain stone for smooth stone anywhere. alpha9697 mixed the two and the farm exploded the moment the dispenser fired.
Put the campfire out before you breed the armadillos. They roll into a ball near the zombie and cannot breed rolled up, which martinbarbier3076 and japper8319 both hit.
Armadillos die to entity cramming once the silverfish start spawning. arandomperson6293 adds a second campfire with its own trapdoors to spread them out.
If the zombie blows up and takes the armadillos with it, move it four blocks further from the silverfish chamber.
Turn the chunk loader off when you are not using the farm. sweetstar383 came back to 54,000 unregistered wither skulls and a badly lagging world.