To be postponed for 1.17 since we dont wanna damage existing worlds.
The handling of hill biomes in the MixinHillsLayer is incorrect. The current implementation is injecting at 4 different points(ordinal is not specified), and is basically copying the random check, again.

It should only be injecting on the 0 ordinal and not duplicating the random check.

The code in question can be found here: https://github.com/CorgiTaco/BYG/blob/11c67ae01baa65c8f1444b66cfe67132c641923a/src/main/java/corgiaoc/byg/mixin/common/world/layers/MixinHillsLayer.java