Minecraft Elegance: Instant Wither Skeleton Farm, No Spawn-proofing 135 skulls/hr (Java 1.16-1.20)

IMPORTANT: If your rates are a lot lower than expected (or you see wither skeletons bunching up along a wall near the golem), lower the portal at the spawning platform by 1 Y level (without adjusting anything else). This fixes a sporadic pathfinding issue.
* In 1.18, rates are about 100 skulls/hour. Be sure to remove sources of light from the spawning platform area, such as torches, fires, and lava. In 1.19, rates are restored to original speed.

FORTRESS FARM UPGRADE AND REFERENCE:    • Minecraft Elegance: Peer Pressure For...  

Discord:   / discord  

FAQs:
"Can the rates be improved with wither roses?" No, wither roses cannot be planted on nether bricks, and nether bricks are necessary to let fortress mobs spawn in the bounding box. Also, the farm is spawn rate limited, not mob cap limited, so wither roses wouldn't help regardless.
"No wither skeletons are spawning." A common build error is to forget to subtract 1 Y level at 7:20. Make sure you are standing on nether bricks to figure out the bounding box; fences don't count. Having multiple nether fortresses next to each other can mess up the bounding boxes.
"Why don't the mobs despawn in the overworld?" A player needs to be present in a dimension in order for the game to make a mob despawn in that dimension.
"What are the rates for coal and bones?" About 3850 coal/hr and 6100 bones/hr.

World download: https://tinyurl.com/2p92tmd4
Zardor's collection system (Join my discord first): https://tinyurl.com/yj8mycup

0:00 Intro
0:24 Materials list
0:52 Farm mechanics
3:54 Finding a fortress
5:45 Get down from the nether roof.
6:48 Determining the outer bounding box, see FAQs
7:35 Build tutorial
13:45 Usage instructions
15:04 MULTIPLAYER INSTRUCTIONS, see pinned comment.
15:36 Advanced fortress finding tips, see description

NOTES
1:20 MiniHuD tutorial:    • How to use MiniHud and Litematica (Fa...  
1:40 This fortress is partially located in a basalt deltas biome, but the farm can still be built in a soul sand valley and is more than 100 blocks away.
2:02 Spawn potential video:    • Minecraft 1.16: Automatic Perimeters ...  
4:11 It is much more common to find a good build site in a soul sand valley than it is to find one in a warped forest. To simplify, you can focus on soul sand valleys.
7:35 Put out any nearby fires and clear any nearby lava around the spawning area to keep light levels low. Temporarily place torches along the outer edge of the spawning platform to limit spawns while you build. (Seeing at least a few fortress mobs spawn during construction is a good sign that the platform works.) Fire resistance and/or invisibility potions will also help.
It's OK to carve away terrain to make the spawning area; just keep 3 air blocks over the platform, and 2 air blocks over the turtle eggs. Make sure there's enough room overhead for wither skeletons to pathfind to the portal, too.
12:25 In hard difficulty, zombie piglins can break wooden doors, so use an iron door with a lever instead.
13:30 The cobwebs slow down the wither skeletons and keeps them aligned so that they don't reach the other portal before the cooldown period ends. The bridge can be shortened to ~7 blocks in length so that the farm starts up faster.
17:08 Increase the productivity by 10% by adding 2 wolves near the southern corners of the spawning platform to scare the wither skeletons out of a blind spot that prevents them from seeing the golem because of the portal frame.
18:16 Example AFK area if pillar X coordinate is odd, instead of even.

ADVANCED FORTRESS FINDING TIPS
Once you've entered a soul sand valley, set down a torch and press Shift+F3 to bring up the debug pie chart. Look carefully at the small text under the chart and then press the number on your keyboard corresponding to "tick". In this case the number is 4, but it might be different on your game, so you should double check. Now press the number on your keyboard for "level", and then "entities". (In 1.16, you need to select "tick" again.) The text below the pie chart will show the list of the entities that have been processed by the game since you started the pie chart. You're looking for blazes and wither skeletons to suddenly appear on this list, which tells you that a fortress must be within 128 blocks of your location.

Press F3+G to bring up the chunk borders and scan the biome in an organized fashion, keeping watch of the pie chart list. When you see blaze and wither skeleton show up on the list, set down a marker and travel about 3 chunks away from the torches around you. (Since the torches mark areas that you've already covered, the fortress must be in the direction opposite of them.) Use the trick at 5:45 to get down from the nether roof.

Huge thanks to Harper for brainstorming ideas for this farm and extensively testing during development.