Beltyn’s Burning Blood

You cause your target’s blood to smolder and boil. You choose one target creature that is not a construct or plant. The target must make a Constitution saving throw, creatures that subsist primarily on blood (including stirges and vampires) or are composed of blood suffer disadvantage on this saving throw. On a success, the target takes 3d6 necrotic damage and the spell’s effect ends. Failure indicates the target takes 3d6 necrotic damage and the spell persists. At the end of each of its turns the target can attempt another saving throw. The damage is reduced by one die each time the target makes a saving throw (i.e. a target suffers two dice of damage after the first successful save). While the spell is in effect, the target cannot regain hit points. The spell ends when its duration expires, the target takes no damage, or the target receives magical healing that is blocked by this spell. Dousing the wound with holy water as an action also ends the spell. If the target of this spell is missing any of its hit points, the damage dice are d12s instead of d6s.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1 die for each slot level above 4th.