Arc of Lightning

Choose two creatures you can see within range who are both within 100 feet of each other. A 10-foot-wide stroke of lightning leaps between the two creatures, dealing 8d8 lightning damage to each creature the stroke touches. Creatures who roll a successful Dexterity saving throw take half damage. 

Using a Higher-Level Spell Slot. The damage increases by 1d8 for each spell slot level above 5.

Adapted from 3e's Complete Arcane.