All Wither Skeletons in Nether

Skeletons that spawn naturally in the Nether are replaced with Wither Skeletons, so the wither-style mobs appear where regular skeletons once did. The change is carried by a datapack, which needs no mod loader to be added to the game, and the author's files cover the loaders listed for this mod.

Of the replaced spawns, about two thirds are Wither Skeletons that carry a bow and the remaining third carry stone swords. The bows give the mobs a use for the vanilla feature that lets them shoot flaming arrows, and Soul Sand Valleys become more dangerous as a result. Wither Skeleton skull farming also becomes easier, since the mobs gather in a more natural way than before.

The datapack is a server-side tool: the server requires it, and players may add it on the client without any effect on joining. It works in the version range 1.21.5 – 26.2, and the author confirmed that the 1.21.11 build works with the older versions. The mod uses no extra boosted spawn odds, so the new mobs appear at the normal rate.