Agitate Blood

Make a ranged spell attack against one living creature you can see within 30 feet, dealing 3d8 magical piercing damage on a hit. The sliver of red energy burrows into your target's body, causing their blood to react violently.

While the spell persists, you may cause the agitant to attack their blood, causing it to squirm and twist violently inside their veins, interfering with their actions.  When you see the target take an action (action, reaction, bonus action, or legendary action), you may use your reaction to cause the agitant to pulse. This deals an additional 3d8 Necrotic damage, and inflicts Disadvantage on the next attack, save, or skill check roll the creature makes before the start of its next turn.