Night and Day

These fighters are blessed by the powers of day or night. But while they are blessed, they must face the consequences. They gain power from one, but weakness from the other maintaining the balance of light and dark in the sky above. The power allows these fighters to stand tall and mighty, but their fall is mighty as well. Night and day also blesses these fighters with a mock of their burning spheres noticeable in their times. The pinnacle of this blessing forms these fighters into the levels of myths but at a dreadful cost.

Night and Day

Starting at 3rd level, Being blessed by day means you are weakest at night. Being blessed by night means you are weakest at day. 

Your unaltered physical modifiers (CON, DEX and STR) determine the extent of your growth.

You maintain any physical proficiencies while in your weakest form and fighting style bonuses, but do not add any physical modifiers to the attack rolls and damage rolls. 

Max hit points use your unaltered Con modifier. Your Initiative, Saving throws and AC amounts and modifiers benefit from the blessing.

Your mental modifiers (CHA, INT and WIS) are unaffected.

Day Blessed

You are blessed by the Day. Double your physical modifiers during the day. Ignore them during the night but gain advantage on Deception and Stealth checks during the night.

Night Blessed

You are blessed by the Night. Double your physical bonuses during the night. Ignore them during the day but gain advantage on Deception and Stealth checks in the day.

Overcome

Starting at 3rd level, as a bonus action, you can become as strong as your blessed form during the time you are the weakest. You gain all bonuses of your blessed form while you are in your cursed form for 10 minutes. You then must take 1d4 long rests before you can use this feature again. 

Cruel Stars

Starting at 7th level, you gain the ability to cast Flaming Sphere at 4th level a number of times equal to your unaltered CON modifier.

Altered CON is your spellcasting ability for this spell. You are immune to the spell's damage. 

At 15th level you gain a powerup and can cast Flaming Sphere at 6th level a number of times equal to your unaltered CON modifier.  

Protective Blessed Pride

Starting at  10th level, gain immunity to the Frightened and charmed conditions and advantage on Charisma saving throws.

The Ultimate One

Starting at 18th level, as an action you can unleash yourself for 1 minute while blessed. While unleashed, you gain the following benefits:
Triple unaltered physical modifiers and damage bonuses.
All creatures within 10 ft when you unleash or that start their turn within 10 ft while unleashed make a Con save equal to your fighter level or take 3d6 radiant or necrotic damage or half as much if they succeed. (radiant if day blessed, necrotic if night blessed)
If you score a critical hit, add another damage die at max damage.
After you use this feature you must take 1d8+2 long rests before you can use this feature again.

Improved Cruel Stars

Starting at 15th level, you gain the ability to cast Flaming Sphere at 6th level a number of times equal to your unaltered CON modifier.

Altered CON is your spell casting ability for this. You are immune to the spell's damage.