Degeneration

With this spell you invert the effects of ordinary healing magic to cause a foe's body to fall apart while they still yet live. You gesture towards a living creature within 60ft of you that you can see. The creature must make a Constitution Save against your Spell Save DC or take [roll]1d8[/roll] necrotic damage at the start of each of it's turns for the duration of the spell's effect. It also has Disadvantage on Saving Throws made to maintain Concentration on spells for the duration, as being degenerated is quite painful.

This effect ends after a minute has passed, if your concentration breaks early, if it is dispelled or if the target leaves the plane you are on.