Source: Planescape - Adventures in the Multiverse

Prerequisite: 4th Level, Scion of the Outer Planes (Evil Outer Plane) Feat.

You can channel cosmic forces of evil to gain these benefits:

Ability Score Increase. Increase an ability score of your choice by 1, to a maximum of 20.
Grasp of Avarice. Once per turn, when you damage a creature you can see within 60 feet of yourself, you can also deal necrotic damage to it. The necrotic damage equals 1d6 + your proficiency bonus, and you regain a number of hit points equal to this necrotic damage dealt. You can use this benefit a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.