A sickly and viscous  green-brown liquid that seems to move unaided.  

When ingested the potions turns the user into an u.dead creature for 8 hours after which they revert to their previous state. While undead the user does not need to eat, sleep, or breath. They become immune to necrotic damage, but vulnerable to radiant damage. 

They are classified as undead for all spells and effects.