You thin, agitate, and accelerate the blood of one creature that you can see within range using dark, forbidden magic.

The target must make a Constitution saving throw. On a failed saving throw, the target takes 4d8 necrotic damage and its blood becomes magically easy to spill. Until the spell ends, the target has disadvantage on concentration checks, and whenever the target takes bludgeoning, piercing, slashing, force, or necrotic damage, that damage is increased by 1d8.

On a successful saving throw, the target takes half damage and is otherwise unaffected. 
Creatures without blood are immune to the effects of this spell.