Minecraft wiki entry for Development_versions, associated text: Crimson forest
A dense forest with huge crimson fungi. Nether wart blocks and fungi are found in patches on the ground and weeping vines are found under the trees and nether wart stalactites.
Zombified Piglins, piglins and hoglins may spawn here.
Soul sand valley
A vast grotto composed of uncovered soul sand, soul soil, large pillars made of basalt, blue fog, and soul fire.
Skeletons, ghasts, and endermen may spawn here.
Warped forest
A color variation of the crimson forest, but with somewhat different vegetation and blue particles and fog effects.
Only endermen may spawn here.