This decorated stein never runs out of rum. It also has four charges, renewed daily. 1 charge lets you See Invisibility. 2 charges let you use Etherealness for 1 round. 4 charges casts Etherealness on you for a minute.
Using any charges requires you to become drunk on the grog, which imposes disadvantage on dexterity checks and saves, perception checks, and insight checks for one hour