Special Mobs

Special Mobs is a mod by FatherToast that adds many new variants of the existing Minecraft monsters. As well as simply adding new monsters, it also tweaks some existing ones. For example, baby monsters will drop items, and Endermen will drop their held item when killed. Skeletons will also be able to hold non-bow tools. New monsters include Fire Creepers, Death Creepers, Doom Creepers, and Jumping Creepers. It adds variants for all vanilla Minecraft mob types, but it's mostly known for its Creeper variants.