Alaskerban's Claws

You brandish the daggers used in the spell’s cast­ing and make a melee attack with it against one creature within 5 feet of you. On a hit, the target suffers the weapon attack’s normal effects and until the beginning of your next, the next source of Lightning damage to strike the target has it's damage increased by 1d4 necrotic damage. 

This spell’s damage increases when you reach certain levels. At 5th level, the melee attack deals an extra 1d8 lightning damage to the target on a hit, and the necrotic damage the target takes from additional sources of lightning damage increases to 2d4. Both damage rolls increase by 1d8 at 11th level (2d8 and 3d4) and again at 17th level (3d8 and 4d4).