Minecraft wiki entry for Undead, associated text: Every individual undead mob in Minecraft.
A group of skeleton horsemen.
A skeleton fighting a spider jockey.
A wither skeleton riding a spider.
A zombie and a husk next to a player.
A zombie siege.
Every mob being ridden by a baby zombie or variants.
Many phantoms.
Skeletons in the Nether.
Tameable skeleton horses.
Three adult husks and a baby husk.