Shinigami, Stage 2 (Death’s Cold Grip)

When you hit with an attack, once per turn, you can choose to deal an additional 3d6 necrotic damage, which ignores resistances, and reduces the maximum hp of the creature by an amount equal to the 3d6 rolled.

This boon is usable a number of times equal to your Wisdom Modifier, resetting on a short or long rest.

Flaw:

Literal Minded. In becoming a creature of pure order, the way your mind breaks down things presented to you changes. You have disadvantage on checks made to solve riddles or puzzles, and tend to take things literally, rather than figuratively.