Mace of Smiting [Булава кары]

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 the mace to attack a construct.

When you roll a 20 on an attack roll made with this weapon, the target takes an extra 2d6 bludgeoning damage, or 4d6 bludgeoning damage if it's a construct. If a construct has 25 hit points or fewer after taking this damage, it is destroyed.

Source: D&D System Reference Document 5.1, © Wizards of the Coast LLC, licensed under CC BY 4.0.