Collapsing Star, Roaring Cannon

As you prepare to release every last fragment of energy from within your being there is a blinding flash of bright blue light, accompanied by a thunderous boom, and a terrifying aura with a radius of 60 feet grows around you. All creatures within this radius must make a Constitution saving throw, each being Blinded, Deafened and taking 3d8 psychic damage on a failed save, or no conditions and half as much damage on a successful one. They must also make a Wisdom saving throw, being Frightened on a failed save and unaffected on a successful one.

Giants beams of lightning emit from your aura, striking random areas in your general vicinity. Make ranged spell attacks for every creature within 6d12 feet. On a hit, a target takes 4d10 lightning damage. Also, wherever these beams hit, the ground is scorched in a 10 foot radius around the impact and transformed into a blazing inferno until the start of your next turn. All flammable objects within these areas are set alight and metal is liquified. If a creature finishes their turn in one of these areas they will take 2d12 fire damage. This part of the spell occurs at the start of the next two turns as long as it is still being cast.

On these next two turns while the attack charges you can take no actions besides this spell, but you have immunity to all conditions and magical damage thanks to the rippling energy surrounding your body. Physical ranged weapon attacks cannot be successfully made against you, as the projectiles are dissolved by your aura, and spells that would otherwise cause you to move from your current space prove ineffective. Also, if any creature starts their turn or moves within 15 feet of you, they will immediately take 10d6 radiant damage and be flung back 60 feet.

On each of your turns up until the final attack you can choose to cancel the spell before it is too late. If you choose to cancel, you will immediately take 5d20 psychic damage and be rendered unconscious for 3 days, unable to be woken by any means. When you awake you will have a -2 reduction to you spellcasting ability score (Intelligence for Wizard, Charisma for Sorcerer).

Finally, on the third turn since the initial casting, you can choose to either complete the casting of this spell or cancel it as previously stated. If the prior option is chosen, you begin to channel all your energy and direct it towards a single visible target within range. Every creature within 600 feet hears the distinct sound of a heartbeat as you begin to slowly raise into the air, the ground below you melting into a molten sludge and the light around you seeming to blacken, as if reality itself is being distorted. Then, in an explosion of vibrant blue and yellow light, a 50 foot high and wide destructive beam of energy is released from within you, flying forward towards the target at the speed of light. All creatures in this area between you and the target must make a Constitution saving throw, taking 8d100 radiant damage on a failed save, or half as much on a successful one.

The target itself takes (20d100)x10 true damage, meaning no resistances, immunities or spell effects can reduce it. If they somehow manage to survive, they are instantly and permanently Petrified. This damage can also not be prevented by Counterspell.

Finally, the planet must make a Constitution saving throw (no modifier), with a spell save DC of 5. On a failed save, it combusts, and the crust is disintegrated within minutes, killing every living thing on and below the surface. The atmosphere is filled with a seemingly eternal fire and the planet will not be habitable again for another 300 years. On a successful save the blast is contained to a radius of 5d10 miles, and the explosion creates a monolithic crater of that size, centred around where you once stood. Its depth is one fifth of its radius. The explosion itself deals 20d20 radiant damage to every creature within its blast radius, and the land within this blast radius is heavily irradiated for 1d8 years.

A full usage of this spell, no matter the effectiveness, causes the caster to immediately die afterwards and all their belongings to disintegrate.