Warriors of Destiny
Potion of Invisibility
(Source: Dungeon Masters Guide, 2nd Edition):
This potion confers invisibility similar to the 2nd-level wizard spell of the same name. Actions involving combat cause termination of the invisible state. The individual possessing this potion can quaff a single gulp—equal to 1/8 of the contents of the container—to bestow invisibility for 3-6 turns.