Corrupting Tendrils

Shoot a dart of dark forbidden magic at a target within range. The target must pass a dexterity saving throw against your spell save DC. On a success, the target takes 1d6 necrotic damage and the spell ends. On a failure, the target takes 1d6 initial necrotic damage, and at the end of each of its turns, the damage doubles. The target takes 2d6 necrotic at the end of its next turn, 4d6 at the next one, then 8d6, and finally 16d6 before the spell ends. This spell is considered forbidden magic. Upon casting this spell, the caster's alignment shifts from good to neutral, or neutral to evil. If the caster is already evil, it is unaffected by the alignment shift.