Meat Cleaver

The Meat Cleaver is a once-per-battle rare weapon in the Butcher set that deals damage equal to 50% of the target's current HP against regular enemies, or roughly 17% against bosses. It inflicts Cleave status on hit and can critically hit — a crit against a non-boss enemy is an instant kill regardless of remaining HP. Backstabbing increases damage further. Best deployed as an opener on a dangerous high-HP target rather than saved as a finisher, since percentage-based damage loses value as HP drops.

Dual Wield grants a free second use on the same turn, letting you potentially remove a regular enemy entirely in one round. Unrestricted converts it to once-per-turn, which sounds powerful but has real diminishing returns — since damage keys off current HP, each subsequent swing on the same target hits for less. Also appears in The Binding of Isaac: Rebirth with the same percentage-damage design.