Mace of Smiting

From Dungeon Master's Guide, page 179. Found on Magic Item Table G.

Description
''Weapon (mace), rare. 4 lbs.''

You gain a +1 bonus to attack and damage rolls made with this magic weapon. The bonus increases to a +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 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.