Crimson Rebuke

Your spilled blood answers harm with harm. The creature that damaged you must make a Dexterity saving throw as blood-red sigils burst around it. On a failed save, the creature takes 4d8 Necrotic damage and can’t regain hit points until the start of your next turn. On a successful save, it takes half as much damage and suffers no additional effect.

If the triggering damage reduced you to half your hit points or fewer, the spell deals an additional 1d8 Necrotic damage.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d8 for each slot level above 3rd.