Potion of Living Death

Potion, rare
  As much as it pains Heliana to admit it, sometimes fighting isn’t an option. With marrow from an undead bone, L’Arsène whipped up this de-vitalising brew, allowing the pair to pass through the Inn’s wight-filled waiting room, hidden in plain sight.
  When you drink this potion, you take on the appearance, smell, mannerisms, and decayed, gravelly voice of an undead creature for the next 8 hours. During this time, undead creatures with a passive Insight of 15 or lower perceive you as undead, and will not attack you unless commanded to by their master. While you are under the influence of this potion, your creature type changes to undead, and you have disadvantage on Charisma (Persuasion) and Wisdom (Animal Handling) checks made to interact with creatures that dislike undead.
  Very rare variant: Increase the passive Insight to 16 or lower. In addition, you gain resistance to poison damage while under the influence of this potion.
  Legendary variant: Increase the passive Insight to 17 or lower. In addition, you gain immunity to poison damage and the poisoned condition while under the influence of this potion