The Cruel Sun

You reach one of your hands upwards to the sky, palm up as if grasping for something. Your will is answered, and you summon a small 30 ft. diameter star above you that remains 150 ft. above your head for the duration. All targets within 1000 ft. of you that you decide that are not behind full cover at the time of casting must succeed on a Dexterity saving throw, or take 4d10 fire and 4d10 radiant damage. All objects being worn or carried, and all creatures you decide in the radius immediately combust and remain on fire. This stacking burn will be referred to as Scorch. If you spend your main action doing anything besides concentrating on The Cruel Sun, it ends as described at the bottom. Your movement speed is halved while concentrating, and if you attempt to teleport or cross dimensions with the spell active, you must succeed on a DC 13 Charisma saving throw to do so first. On a failure you remain in place, and your transportation ability is not consumed. If you teleport, you teleport with your sun, or it follows you into the new dimension. Traveling back to the original plane does not cost a saving throw.

Creatures that remain on fire take stacking, additional damage each time the sun pulses out and are Scorched. On your future turns, as well as initiative count 0 (losing to ties); the sun pulses out again. Each creature still within line of sight takes an an additional 2d10 fire and 2d10 radiant damage, and a stack of Scorch. While in range of the sun, creatures take Scorch stacks without making a saving throw. Each creature that does not take full cover stacks damage each time, taking 4d10 fire and 4d10 radiant on the second pulse, and 6d10 fire and 6d10 radiant on the third pulse. Scorch stacks indefinitely. 

Targets will continue to take their current stack of Scorch  damage at the start of their turn, even if they are in full cover or outside the radius of the spell. Only when a target is behind full cover from the sun by physical or magical means or outside of the radius, they can then make a Dexterity saving throw against your spell save DC. On a success, they remove all stacks of scorch.  On a failure, they take their current stack of Scorch damage they were at. When they end their turn in the sun or spend more than half of their movement in line of sight of the sun, they add another stack of Scorch, starting at the first level of 2d10 fire and 2d10 radiant. A creature in a water based environment or with the ability to douse themselves, or with fire immunity automatically pass the save, but will still continue to take stacks of Scorch.

Finally, when you end the spell by will or by the duration being exceeded, all targets within the area must succeed on a Dexterity saving throw against your spell save DC. On a failure, targets take another 4d10 fire and 4d10 radiant damage, or half on a success. Even after your spell ends, all creatures and objects remain on fire until doused or until targets succeed on a saving throw, taking damage of their last Scorch level until it is cleansed.