Drevet’s Arcane Cataclysm

When you cast this spell it requires you to gather energy around you and release it into a beam of energy. When you begin to cast this spell you cannot use any movement. When you release the energy it blasts out in a 15ft wide and 300ft long beam. Every creature within the beam must make a dexterity saving throw or take 25d8 force damage on a failed save or half on a success. 
after casting this spell the caster must make a constitution saving throw DC18 or be stunned for 1D4 rounds.