Fallen_Breath | Universal Skull Farm MCJE 1.13.1+ @FallenBreath | Uploaded 5 years ago | Updated 3 hours ago
You can get all of the four types of renewable skulls in this farm: zombie's, creeper's, skeleton's and wither skeleton's.
Use channeling trident to get a lot of charged creepers in the thunderstorm, use the skeleton to automatically ignite the creepers.
The wither skeleton farm in nether doesn't need to be as efficient as in the video. Just adjust the afk point (such as youtu.be/OooHSzAK6v0), and it's ok to not clear the nether.
The priority of charged creeper blowing off the skull is stable, relative to the relative position of the bombed mob, the direction of the chunk, so the farm is diretional. (20190101update: In fact it controls the order of mobs entering a subchunk to control the skull dropping priority. More detail: youtube.com/watch?v=t1jVfcxfeyM)
Processing period: 5.8s; efficiency: 10.3 head/min (max)

[Some problems that may arise]
There is a small probability that the skeleton will be too sluggish to shot before the next couple of skeleton and charged creeper comes.
If mobs are not processed in time, they may get suffocation damage and the skeleton kill the creeper in a shot.
Both of the above problems will not mess up the farm, only reduce its efficiency.

WDL drive.google.com/drive/folders/1aI-_vLPH4B7ErjNC06FhWy9HU2EBsb5R?usp=sharing
Version: Minecraft Java Edition 1.13.2
Shaderpacks: Sildurs Vibrant Shaders v1.19 Extreme-VL (cover)
Resourcepacks: Faithful-1.13.2-rv1

bilibili: bilibili.com/video/av39481156