DND 5th Edition

Source: Dungeon Master's Guide

Weapon (mace), rare

You gain a +1 bonus to attack and damage rolls made with this magic weapon. The bonus increases to +3 when you use this mace 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 an extra 14 bludgeoning damage if it's a construct. If a construct has 25 hit points or fewer after taking this damage, it is destroyed.