ADVICE: This mode requires very good gear (and some rng) if you are aiming to clear highest difficulty in first attempt. So, if you don't have the required gear, don't waste time trying hardest mode and focus on whatever mode you can do. You will gain points which will make fights lot easier in future.

Blessing of the Stars : It gives buffs to specific constellations which makes fight easier. You unlock bonus effects by assigning heroes to slots. Initially, only 1 slot is available per constelllation. By beating bosses, you gain points to unlock more slots to assign heroes. Perdition gives 4 points, Nightmare gives 3, Hell gives 2, and Hard gives 1.
Note: The heroes assigned in these slots can't be used in the fight.
For ex: Here, I have 3 slots unlocked after getting points from beating boss. Another important thing is you might notice the buff doesn't activate like in image below. It is because it also depends on the Level, Awakening, Artifact and Gear Score. Try putting better gear on your units if your points fall short.


The order of bosses done is Fire -> Ice -> Earth.
Earth boss requires level 2 blessing, othwerise it is impossible to clear the fight.

NOTE: For each boss, you will see a constellation gauge or the moon gauge. Your aim is to keep the percentage of moon near 0% to make fight easier. Every boss has their own mechanics of increasing and decreasing it.

Boss 1: Fire Trial 

Team: Fenne+Imprints.  
Fenne can't be replaced, but you can choose other imprints. Choose imprints that give flat hp or attack. Furious helps alleviate crit chance requirements too. (Dont put any gear on imprints)
 


Gameplay

• Start with battle with auto and imprints skills off. (imprints will die and fenne will solo from there).
• Be careful near 70% HP. Near 70% HP, boss will kill you, so you want to save Fenne S3 to use after she revives.
• When near 40% HP, hit the boss only till you are just above 40%. Then s1 one of the mobs. Then s1 the boss. After that, can again auto.
  Tip: If you are having issues with Fenne solo, can build Blue Tywin, make him tanky and place in the front. Tywin has defbreak which helps keep constellation energy low.
  
  Boss 2: Ice Trial
  
  <p>
  Team: Senya + Roana + Violet + Charles
  Alternate Teams: Laika / Ray + Roana + Charles + Violet, Senya + Roana + Charles +  Ervalen
  </p>
  
  
  
  
  
  Gameplay
• The trickiest part of this fight is if any of your unit is at 10% or less CR at the end of the boss' or the miniboss' turn, they will be fully stripped and unbuffable for 2 turns. If you having constant issues with this, try adjusting speed tuning slightly.
• The constellation energy decreases whenever you counter the boss. So Charles and Violet/Ervalen keep it low. If you are stuggling to keep it low, try putting counter set on senya and roana too for additional chances to counter.
• Soulburn Charles S3 every time.
  
  Boss 3: Earth Trial 

NOTE: I cleared this boss on nightmare level. I didn't have the gear nor the patience to keep trying it for hours cause of rng. This fight requires landing consistent burns on the mobs to kill them, but for that you need a maxed Hwa artifact to reduce rng. On top of that, Fire yufine has 15% innate crit chance+15% additional crit chance cause of elemental advantage, so there was a 30% chance to crit and artifact burn doesn't proc if you crit. If you want to try perdition, it is almost same stats but slightly better mainly on H.Yufine.

Team : H.Yufine + Schuri + Beehoo + Sol / Fire Tieria.

Gameplay

• The constellation energy or moon gauge increases by 5% every turn taken by anyone and an additional 5% for every attack the boss or the ads use. The gauge decreases by 15% every burn the boss receive and if it reaches 100%, the boss immediately get an extra turn which will wipe you.
• Phase 1: Burn mobs, kill them
• Phase 2: The boss summons bigger ads which now heals the boss. Just need more burns to land on mobs to kill them.
• Phase 3: Boss does not heal itself anymore and you want to reduce its HP to 0 or as close, otherwise boss takes final turn and wipes your team.
  So, basically just land burns, kill mobs and you win.
  
  If you have any questions, can leave in comments.