Set

You can use a bonus action on your turn to prepare, or "set," a set weapon against a foe moving toward you. A weapon becomes unset if you move or take any action after setting it. If a target enters your reach while you have the weapon set, you can use your reaction to make a melee attack with the set weapon against the target. If you hit, and your target moved 20 feet or more toward you before the attack, you can roll one of ht weapon's damage dice one additional time and add it to the damage total.