Undead refer to mobs that are considered undead. Undead mobs share certain traits: they are healed by Potions of Harming and harmed by Potions of Healing, and the Wither will not attack them (except that the Wither attacks wither skeletons[Bedrock Edition only] ). Undead mobs are also weak against the Smite enchantment.
Most of them burn in sunlight, can pick up and use items, and all of them wear their own armor (zombies, skeletons, wither skeletons and zombie pigmen can wear actual armor, zombies, zombie pigmen and withers have extra natural armor, withers have their shields they use when below half health, zombie and skeleton horses can wear horse armor,[verify] and phantoms don't actually have any armor, but their agility makes up for it).
All undead mobs, will sink when in water.[upcoming 1.13]