Embolism

You disturb the circulatory system of a creature within range, causing clots to form. Make an intelligence saving throw. On a failure, the creature takes 1d6 necrotic damage, and the first time it makes a saving throw before the end of your next turn, it must roll a d4 and subtract the number rolled from the save.

This spell's initial damage increases by 1d when you reach 5th level (2d6), 11th level (3d6), and 17th level (4d6).