Armor of the Last Guardian (5e Equipment)

Armor (plate), legendary (requires attunement by a cleric or paladin) While wearing this armor, you have a +2 bonus to your AC, and when a fiend or undead that you can see attacks a target other than you within 30 feet of you, you can use your reaction to impose disadvantage on the attack roll. Alternatively, if a fiend or undead that you can see forces a target other than you to make a saving throw, you can use your reaction to grant that target advantage on the save.