Surtr's Dawn Damnation

"Only blood can satisfy Surtur... and very few can call the Sun into the palm of their hand...."
- Archmage Nox. 

With an outstretched hand, you mutter the ancient true name of Surtur causing the Sun to vanish from the sky. Ancient Giant runes blaze into your flesh, scarring your entire body without any pain. In a flash, the blazing solar orb then reappears within the palm of your hand leaving the rest of the world in darkness. Make a melee spell attack against a creature you can reach. On a hit, the target takes 4d10 bludgeoning damage, 16d12 radiant damage and 30d6 fire damage. On a miss, the target takes no damage. This damage ignores resistance and immunity, and can’t be reduced or avoided by any means. A creature reduced to 0 hit points by this damage disappears in a blinding flash and is destroyed, leaving only magical possessions behind. This impact creates a 100-foot-radius sphere of fire from the point of impact for 1d4 rounds. When a creature other than you enters this impact's area for the first time on a turn or starts its turn there, that creature must make a Dexterity saving throw. A creature in this area takes 8d6 fire damage and is blinded for 1d6 hours. 

The fire spreads around corners. It ignites flammable objects in the area that aren't being worn or carried.

Once the attack has been made, the Sun once again returns to the sky now an hour behind its normal placement on a hit. On a miss, the Sun does not return for 1d8 days, causing all that die in this time to rise once more as an undead. Spells that relate to fire also only deal half damage in this time as well. 

If you happen to miss the target, the spell is performed indoors/at night or the setting has no sun to speak of, the spell backfires on you, trapping your soul in a volcanic rock located deep within the Plane of Fire while vaporizing your body, leaving only magical possessions behind.