The Hand of the King in Yellow

Attunement. Cut off one of your hands at the wrist and press the artifact to the stump; it grafts on and works as your own. If it is ever removed, you die.

You can't be charmed or frightened.

Your Intelligence increases by 2 (maximum 24); your Charisma becomes 6 unless already lower; your Strength becomes 20 unless already higher.

You have disadvantage on saving throws against poison.

Melee spell attacks made with the hand, and melee weapon attacks with a weapon it holds, deal an extra 2d8 cold damage.

Rot. Over four days your body rots: hair, then fingertips and toe tips, then lips and nose, then ears. Only regenerate restores them; mechanical parts rust and corrode instead.

Any attempt to destroy it seems to work, but it reappears in a hidden place to be found again.

Olaf's gauntlet. Rebuilt with his Armorer's thunder gauntlet, it acts as a greatclub with booming blade.