Arcrean's Arcbolt

Calling forth your own soul as fuel, you summon forth the full might of the storm within you and concentrate it into a white, blinding branch of searing lightning that shoots forward in a direction of your choosing in a 60ft cone. Every creature within the cone must succeed a DEX saving throw or take 20d6 lightning damage, or half that on a success. Each creature who fails the saving throw is now tethered to the caster by faint static lines, paralyzing them. While maintaining concentration, the caster must use their action to deal another 20d6 lightning damage to each creature tethered. Each time a creature dies, the concentration timer resets. Each turn concentration is maintained, the caster takes 10d6 lightning damage, cannot move and is blinded and deafened. Each creature within in or within 15 feet of the cone must make a CON saving throw or be blinded and deafened for 1 minute. Tethered targets are freed of all status effects if the tether is broken. 

This spell cannot be voluntarily stopped. When concentration is broken the caster falls prone from weakness and takes an immediate 4 points of exhaustion.