Black Belt (5e Equipment)
From D&D Wiki
Wondrous item, legendary (requires attunement by monk or fighter)
Passed down by the greatest monks of time, this jet black belt has golden runes on it, and allows the wearer to pull off insane attack combos and almost always score critical hits.
Devastating First Blow. The first melee attack you make every turn will score a critical hit on a roll of 19-20 on the d20.
Counterstrike. While wearing this belt around your waist, you may counterstrike a creature that hits you. When you are hit by an attack by a creature within 5 feet of you, as a reaction, you gain a +4 bonus to AC against the triggering attack. If the attack misses, you can make a melee attack against the creature that attacked you.
Combo Attack. At the start of your turn, you may activate Combo Attack, which lasts until the end of your turn. Every time a melee attack hits a creature this turn, your next melee attack this turn deals 1d8 additional damage of the same type as your weapon. This effect may be used 2 times, and the black belt regains all expended uses at dawn.
Brutal Blows. While wearing this belt, whenever you score a critical hit with a melee weapon attack, you deal 1d6 additional damage of the same type of this attack damage.
Stone Breaker. Your unarmed strikes deal double damage to objects and structures.