Soul campfire mob farm

A soul campfire mob farm by TheySix, built over an ocean. Eight stacked spawning platforms flush with dispensed water into a central column, soul sand rings stop spiders climbing back out, and a bed of soul campfires at the bottom does the killing into twenty chests. The whole thing runs off one lever on a redstone clock. It is cheap for its size at roughly 3,000 building blocks, and it is the drops rather than the XP that it is built for.

• Witches ruin it. They drink fire resistance the moment the campfire touches them and then sit in the kill area taking up the mob cap. dapmer3116 and akakemushi439 both report it and nobody offers a fix.
• Spiders cling to the walls instead of dropping. The soul sand rings exist to stop them climbing, and huyphamle159 adds buttons wherever they still manage it.
• The AFK height in the video is too high. braydenphillips4272 found mobs despawning before they reached the campfires at 110 blocks above the lowest platform, and dropped to 50 above the farm roof to fix it.
• oran0reef's packing list: four shulker boxes holds the whole build, bring a bed so phantoms leave you alone, and bring more than the 128 temporary blocks the list allows.
• Take the temporary torches out when you finish. Two builders forgot and got nothing at all.
• Wither roses in place of the soul campfires raise the output noticeably, which Random_user_8472 and killerfilda2755 both recommend.