This guide is for those that want to kill Angolmois for the second timeafter the true final boss brings him back. I decided to make this guide after 2 hours trying to kill him and failing miserably until I used Balin spam.

The mission Angolmois appears is one of those missions that only the selected participants can fight in. Thankfully, the requirement for this mission is low and most of the characters you need will fill fill 80% of the requirements. You just have to add two more characters and it's done. The characters you want to use for this strategy are: Main Character, Himiko, Rasputin, Tutankhamun, Beethoven, Palamedes, Balin, plus two others.

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The main character needs Outenta and Mikazuki Munechika. He needs these so he can deal decent damage and earn brave with crits. His job is to advance and attack the boss when possible if there aren't enemies he can hit.
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Himiko needs Emerald Tablet and Almagest. This is to start at least with 1 brave and every time Himiko gets a turn, she gets 1 brave. It essentially makes a free heal. Her job is to remove the devastating debuff this boss fight has and heal when possible.
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Rasputin doesn't need these items but they are what I had when fighting. Cauldron of Rebirth and Lia Fail. Rasputin's job is to take hits and heal anybody that needs a big heal
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Tutankhamun uses Yasakani no Magatama and Rosetta Stone. Her job is to grant as many brave balls as possible per turn since there will be a lot of healing and brave use. Her job is to use her AOE heal because the boss spawns many boomerang enemies.
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Beethoven is a free item slot. I gave her speed +1 so that she could move more often but you can probably give her anything else that you think might work. Her job is attacking the boss or any other enemy that moves before Balin.
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Palamedes needs Sibylline Books and Tetrabiblos. They give you more brave at the start and per turn. Her job is to cast defense up on herself, Himiko, and Balin so they don't die by an attack that might sneak in.
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Balin is the MVP of this battle. I'd say she's absolutely necessary to survive. She needs two items: Laevateinn and Pandora's Box. Pandora's box allows her to move twice in a row in her first turn and Laevateinn is to generate enough brave for another Keneruchyn. Her job is to use Berserk and then use her Hero skill to kill everybody in the enemy area.
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What makes this boss horrible and annoying is that the heroes in the battle start with a debuff of -5 to all stats. This makes your attacks hit like a wet noodle and your defense like a sheet of paper. The boss also spawns an infinite amount of enemies that have high defense and decent attack. When the boss spawns enough enemies, it will start attack using his special skill. By the time this happens, most of your characters will be dead or a normal strategy will fail. The point of this strategy is to kill all of the enemies he spawns before they get to attack to stun lock the boss into using his brave for summoning allies. You could try to kill the enemies one by one but that takes too long and the enemy area will fill up quicker than you think. This is where Balin comes in. Balin's Hero skill, Kenuerchyn, can hit the entire enemy are for a nice amount of damage. Combine that with Berserk and she'll one shot all of the enemies minus the boss. However, we don't put Balin in the battle. We use the MC's Hero skill to summon Balin into the battle, which avoids the -5 debuff.

First you wanna start your formation like this:
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This formation makes it hard for the enemies to hit more than 2 heroes at the same time. It also buffs Rasputin, Tutankhamun, and Palamedes with +2 defense. Beethoven will give Balin +1 speed which is crucial, and Himiko give double healing to the MC.

After starting the battle, Angolmois will attack the character with the most HP in the right column, which will be the MC. You want to heal with Tutankhamun and when Himiko gets her turn, you want to refresh the first column so that other attacks do not kill Rasputin and the MC. Then you want to advance with Rasputin and the MC so that the boss cannot spawn any enemies on the buff tiles and it allows everybody to hit the boss.
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You want to avoid attacking with the MC to avoid gathering hate on him and giving the boss more brave. Only attack with the mages to generate brave and Beethoven can postpone his turn. The next time Himiko gets a turn, you want to use Refresh on the middle column to avoid Himiko and Palamedes dying. You want to try getting 10 brave as quickly as possible before the boss spawns more than 1 enemy. Once you have 10 brave and it is the MC's turn, use his Hero skill and summon Balin on the middle left square so she can hit everybody in the enemy area and get +3 attack from the tile buff.
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Once you summon Balin, she will instantly get her turn. Since you don't have any brave, you have to wait 2 times (hopefully 3 times if Balin is fast enough) to generate brave. This is the most dangerous part of the strategy because you have to wait for Balin to get another turn to use Berserk and wait for another turn to use Keneurchyn. This is where you'll be using Tutankhamun's AOE heal, Rasputin's powerful heal, Palamedes' defense buff, and Beethoven's speed buff. You want to use Palamedes' and Beethoven's buff in the center square so that it covers Himiko, Palamedes, and Balin. You NEED to use Berserk before Keneurchyn to deal enough damage to the other enemies. Avoid trying to use Doping as it will most likely get you killed. If you managed to get to this point, then all that is left is to spam Balin's Hero skill every turn she has because her skill will generate enough brave for another one if she hits an enemy that she doesn't have the advantage against. However, you need to be careful because the boss sometimes can spawn enemies that will move before Balin, this is why you need Beethoven. Her normal attack and Hero skill postpone an enemy's attack which allow you to not lose Balin or make her attacks weaker. You want to keep attacking Angolmois to postpone his enemy summon or attack an enemy that moves before Balin. If the enemy isn't in range to attack with Beethoven, then you'll have to hope that Balin can survive or else you will lose the battle.

This will take a long time because Balin won't be doing as much damage as Achilles with Futsumitama or Yoshitsune with Futsumitama if you don't crit, but it will guarantee that you don't get overwhelmed with enemies. You can also hit the boss with the MC and the other mages if you don't need any healing or to reapply the buffs. You also want to try and get Himiko to remove the debuffs on the left column in case an enemy decides to attack Beethoven or Tutankhamun.

Thank you for reading this guide. I hope that it helps you defeat this annoying boss that should have been saved for post game