Undead

Poison Immunity: Virtually all undead – probably because they don’t have any blood left to contaminate – pay absolutely zero attention to poison damage and poisons. Condition Immunities: Much like poison, being dead relieves many creatures of the drawbacks of, well, living.
Many undead monsters are immune to conditions like Charmed, Exhaustion, and Poisoned. Rarely do the undead require sleep, food, water, or even air to breathe.
Mundane Damage Resistance and Immunity: The undead also tend (whether it’s the result of just being big and beefy or having no corporeal form to hit) to resist or flat out ignore bludgeoning, piercing, and slashing damage.
The notable exception here is damage coming from either magical or silvered weapons.

Skeletons and Zombies: The Horde

Whether they’re restless guardians of a forgotten tomb or the shambling servants of an evil necromancer, zombies and skeletons are an evergreen, highly versatile option for any undead-based encounter