Annihilation

You scream. Dark energy swirls around your eyes, making you look almost demonic. Hundreds of black beams shoot from your body like dark sun rays, slicing into your enemies like lasers, and making it look like you're exploding. When the beams hit the ground, they explode in black flames, injuring and destroying anything within a 10 ft. radius around the point of impact, literally burning the ground and shredding it to pieces. If a creature with 70 HP or less is hit directly by a ray, it is instantly turned into black mist. Creatures hit directly that have over 70 HP make a DC 20 Dexterity saving throw. On a successful save, they are not harmed. On a failed save, they take 8d10 Void damage. Creatures within the range of the explosion make a DC 15 Dexterity saving throw. On a success, they take 2d10 fire damage, ignoring resistance and immunity. On a fail, they take 4d10 fire damage, ignoring resistance and immunity.

The explosions caused by the beams blast up fiery missiles, these arching high in the air before hitting the ground, exploding, and sending up more missiles, repeating until stopped. These missiles explode on impact, blowing up a 15-foot radius circle around them. If a creature with under 30 HP is directly hit by a missile, they die instantly. If a creature with more than 30 HP is directly hit by a missile, they make a DC 15 Dexterity saving throw. On a success, they are dealt 2d10 fire damage (ignoring resistance only) and are knocked backwards 10 feet. If they fail, they take 7d10 fire damage (ignoring resistance only) and are knocked back 15 feet. If a creature is in the zone of the explosion, but is not directly hit, they make a DC 15 Dexterity check, taking 2d10 fire damage (ignoring resistance) on a success or 3d10 fire damage (ignoring resistance) on a fail. 

Any terrain within the zone of an explosion is  ripped apart a burned, becoming difficult terrain. For 5 hours after the explosion, any creature that enters it takes 1d4 fire damage per round inside it. When the caster is cast the spell, a void portal spell will be activated around them, teleporting them to a demiplane in the Void, where they will be healed (unconscious) for 2 weeks. This costs the caster 20 Void Points, and can only be used twice in a lifetime. 

The missiles will continue exploding like this for up to 24 hours, enough to wipe out an empire if not stopped. The fires can be put out be water or magic, and any missile that lands in a very wet area will not explode. Missiles can only land within 50 feet of the explosion that launched them. They cannot pass through solid or water barriers, making barrier or water based spells such as wind wall, wall  of water, shape water, very useful for stopping the effects.