Minecraft wiki entry for Development_versions, associated text: Hill biomes
More hills variants to fit with the new biomes.
Birch forest hills, cold taiga hills, and mega taiga hills can now be generated.
M biomes
Variants of other biomes with an "M" added to the end of them.
Much rarer than their normal biome or any of its other variants.
Extreme hills M, taiga M, roofed forest M, extreme hills+ M, savanna M, mesa plateau M, and mesa plateau F M are more mountainous versions of their normal biome.
Swampland M, jungle M, jungle edge M, birch forest hills M, cold taiga M, and savanna plateau M are other rare biome variants.
Desert M contains patches of water, unlike normal deserts.
Birch forest M has taller birch trees than usual.
Plateau biomes
Variants of other biomes with "Plateau" added to the end of them. All of them are like their normal biome or its variants, but flattened at the top.
The only plateaus in the game are savanna plateau and mesa plateau.