Source: Dungeon Master's Guide
Wondrous Item, Rare (Requires Attunement)
While wearing this belt, you gain the following benefits:
Dwarvish. You know Dwarvish.
Friend of Dwarvenkind. You have Advantage on Charisma (Persuasion) checks made to interact with dwarves and duergar.
Toughness. Your Constitution increases by 2, to a maximum of 20.
In addition, while attuned to the belt, you have a 50 percent chance each day at dawn of growing a full beard if you can grow one, or a thicker beard if you already have one.
If you aren’t a dwarf or duergar, you gain the following additional benefits while wearing the belt:
Darkvision. You have Darkvision with a range of 60 feet.
Resilience. You have Resistance to Poison damage. You also have Advantage on saving throws you make to avoid or end the Poisoned condition.