You draw out your blood, turning it into rain that pours down over a 30-foot radius area. As you cast this spell, you must expend a number of hit points. A creature that starts its turn within the rain must make a Dexterity saving throw. On a failed save, a target takes 4d6 + half the number of hit points spent as necrotic damage, and its movement speed is slowed by 5 feet for the duration of the spell. On a success, the target takes half damage and is not slowed. The slow can stack with itself, but it cannot reduce a creature’s speed below half.