Wondrous Item, rare (requires attunement by a Monk, Barbarian, or Fighter)
This pair of brass knuckledusters looks somewhat mundane, except for an engraving reading The Champ. Once per long rest, when dealing damage with an unarmed attack, you can choose to expend all charges stored in the knuckledusters to deal an additional Nd8 Force damage, where N is the number of charges expended (e.g. expending 3 charges lets you deal an additional 3d8 Force damage), at which point a spectral and translucent boxing glove surrounds the wielder's fist.
Stores a maximum of 3 charges. Charges are reset to zero at the start of combat. Dealing damage against an enemy with an unarmed attack grants a charge. You must expend all charges when using the item's abilities.
Notes: Monk, Barbarian, or Fighter