Arasthula's Withering Smite

The next time you hit a creature with a weapon attack before this spell ends, the target is left with a sickly black mark where the weapon struck them. The attack deals an extra 2d6 necrotic damage to the target. The target then takes an extra 1d6 necrotic damage at the end of your turn, followed by an additional 1d6 necrotic damage at the start of their next turn and a final 1d6 necrotic damage at the end of their next turn.
The creature can avoid the extra damage if the spell ends early.