Eldenfel's Retribution

You draw electrical energy to unleash a powerful blast of death and destruction. For the first four turns of casting, any lightning or electrical attack/spell within 120 feet doesn't take effect and is instead consumed in the charging of impending doom. On the fifth turn, every creature in a 10 feet wide line must make a DC 17 dexterity saving throw and take 50d20 lightning damage on a failed save, or half as much on a successful save. For the purpose of this attack, lightning damage immunity is considered a resistance.