Arrow of rot

A sickly black arrow streaks toward a target within range and melts into their skin. Make a ranged spell attack against the target. On a hit, the target takes 4d4 necrotic damage immediately and 2d4 necrotic damage at the end of its next turn. On a miss, the arrow deals half as much of the initial damage and no damage at the end of its next turn.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage (both initial and later) increases by 1d6 for each slot level above 2nd.