Animus' Hemoparasite

You create a deadly javelin out of your hardened blood that possesses its targets blood. Select one creature within range. Make a ranged spell attack against that target. On a hit, a target takes 6d12 piercing damage. If the javelin misses, or the target does not have blood, the spell ends.

If this javelin hits, your blood enters the targets bloodstream and eviscerates them from the inside out. At the end of each of that creatures turns, it must make a constitution saving throw. On a failed save it takes 4d6 necrotic damage, and half damage on a success.