Piercer
Melee Weapon, rare (requires attunement)
You have a +1 bonus to attack and damage rolls made with this magic weapon.
A character attuned to the sword regains the maximum possible number of hit points from expended Hit Dice. However, the attuned character must eat twice as much food each day (a minimum of 2 pounds) to avoid exhaustion (see “The Environment” in chapter 8 of the Player’s Handbook.)
Source: Acquisitions Incorporated p. 121