Mace of Smiting
Source: Dungeon Master's Guide
Weapon (Mace), Rare
You gain a +1 bonus to attack rolls and damage rolls made with this magic weapon. The bonus increases to +3 when you use the weapon to attack a Construct.
When you roll a 20 on an attack roll made with this weapon, the target takes an extra 7 Bludgeoning damage, or 14 Bludgeoning damage if it’s a Construct. If a Construct has 25 Hit Points or fewer after taking this damage, it is destroyed.