Made a few mistakes in the run but still managed the clear. Some tips
1. I set Onion Knight call on Pecil for the damage, utility and granting of free skills
2. If the boss is near a full recast, try not to kill off the maria manikin. The recast attack will revive the manikin to full HP if it's dead. But if the manikin is still alive it only heals her for 50k hp.
3. I accidentally got petrified by the wyrm- try your best to prevent this, the game tells you to stack brave as a warning. If you do get petrifed, the petrification will be undone if the character gets broken again
4. diabolos summon is key here. The blessing it gives is great, but moreover there is a time in the fight where the boss will use Invert and grant itself a range of buffs, chief of which is a hp regen that heals a whopping 700k hp a turn. Once the boss buffs itself pop Diabolos summon and it will dispel all buffs.
2