End portal obsidian farm

Shulkercraft's build tutorial for Scorpio's wither obsidian farm, and the one most people find first. A wither trapped in the End keeps destroying the end portal's obsidian while a snow golem in the overworld fires snowballs through the portal to keep it working, and the game regenerates the obsidian instantly. It works and has done for years, but it has accumulated more version fixes than almost anything else in the library, and the comments themselves suggest an easier farm at the same rate.

• Replace the glass with obsidian or crying obsidian. The wither breaks glass easily and escapes, and the front row of glass on the cobblestone generator also lets water pour through and stops the farm.
• Put the snow golem on a bottom slab, or an enchanting table, so its snowballs reach the wither instead of sailing over the portal or hitting the zombie. This is the most reported fix and applies from 1.20.2 onward.
• The chunk loader is the dated part. Builders swap it for a newer design, face the portal south when the minecart sticks, and use lava where the video uses cacti.
• Five observers and two detector rails are missing from the item list in the video.
• Add glass around the water, or obsidian occasionally drops out of the collection system.
• To switch the chunk loader off, put a lever on the block holding the redstone torch. The original designer posts the safe order for killing the wither in the same comment.