Universal Undead

In short, every type of climate should have it's own undead variants

Humid Climate: (Jungle, Swamp, and similar)

The Bogged should spawn in all humid biomes (more often than Skeletons) with it's own variant of the skeleton horse to match the aesthetic. For it's unique functionality, it should leave behind a noxious trail effecting the player with nausea. The Zombie could be copy pasted from Minecraft Dungeons (Jungle Zombie). Unfortunately I don't have good ideas for Zombie mounts. I need help on those.

Dry Climate: (Desert, Mesa, and similar)
The Husk should spawn in all dry biomes (more often than Zombies) with it's own variant of the Zombie horse to match the aesthetic. No unique functionality that I could think of. The Skeleton and Skeleton Horse are already very dry and I see no need to change them here.

Ocean: (Reef, Deep, and similar)
The Drowned already spawns here exclusively, great! It's new mount, the Nautilus, is looking awesome, yay! The Skeleton here should, not could, should be copy pasted from Minecraft Dungeons (Coral Skeleton). They look awesome and just make so much sense.

Cold Climate: (Taiga, Snowy Planes, and similar)
The Stray should spawn in all cold biomes (more often than Skeletons) with it's won variant of the Skeleton horse to match the aesthetic. For it's unique functionality, players within a short radius of the horse are effected by the freezing effect. The zombie can be copy pasted from Minecraft Dungeons (Frozen Zombie).