Widows Smite

The next time you hit a creature with a weapon attack during the spell’s duration, your weapon flares with darkness and malicious intensity, imbuing the attack. The damage deals an extra 1d6 necrotic damage to the target and causes the target to be wreathed in darkness. 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the initial extra damage dealt by the attack increases by 1d6 for each slot.

A homebrew creation by MrtheMarshal - you are welcome to use, but please check with your DM first