Eldritch Hex

You place a hex mark on a creature that you can see within range, and the target must succeed on a Wisdom saving throw or become hexed. The target takes an extra 3d6 necrotic damage whenever you hit with an attack. Choose one ability when you cast the spell. The target has disadvantage on ability checks and saving throws made with the chosen ability score for the duration of the spell. Additionally, while hexed, the target has disadvantage on all attack rolls against you. Lastly, while the target is hexed, it must make a Wisdom saving throw at the start of each of it's turns. If it fails, it wastes its action that turn doing nothing.

If the target drops to 0 hit points before the spell ends you can use a bonus action on a subsequent turn of yours to hex a new creature.

A remove curse spell ends this affect. At the DM's option you may choose an alternative curse effect, but it should be no more powerful than the description above. The DM has final say on such a curse's effect.