Okay, after having spent over 2 hours of praying to RNJesus and changing setups more than my underwear, I finally found a setup that was able to beat that stupid thing.
First of all, let me say this: Just try often. I rebuilt setups from the Internet which failed to work for me because the fire attack WILL kill you no matter how much you turtle and the bomb attack might kill you or might not. I guess it doesn't have fixed damage but rather a damage range, so just keep trying. Dear thread viewers who have also beat the quest, feel free to share your solutions and comment so we can offer as many solutions as possible to make the quest beatable for as many people as possible.
My setup:
Fenrir Lvl. 31
HD Vanitas (put any copy medal here) - ATK Boost 5 - traits: def+2000 (dunno whether it made a difference)
Kairi EX - Second Chance 3 - no traits
HD Zexion - ATk4 Gauge 0 - strength+2000 and ground def, but doesn't do much damage anyway, so don't bother
Key Art Sky - defense boost 3 max - ground and Extra Attack
Warrior of Light - ATK Boost 5 Gauge 1 - no traits
HD Leon - ATK 5 Gauge 1 - +2000 strength
You WILL need defense boost 3 max. You don't need to use your EA 40 copy medal on Kex, use it on a turtle medal or strength reduction medal (in my case, Zexion). I used WoL and HD Leon here because they have the highest damage output of my medals right now due to the boosters, I guess everything's fine as long as it does damage. Ava might also be a good choice, I can't test it because I don't have her. The secret of the setup is that it doesn't waste a slot for a dispel medal - I tried a lot of setups with one that all failed because you can remove the status buffs he already did, but he will buff himself right before his attack so you can basically not defend yourself against that. Try to get a decent defense up and his attack down and try to deal around 500-600 bars of damage each round because you have to reduce the turns. He'll spit fire at his first turn and you won't survive that, you can't survive the fire, so you basically have to survive the bombs and hope that he doesn't attack you with fire more than twice. The problem with most all-turtle setups is that they drag out the fight for too long - the enemy has too many turns to buff himself up or maybe use the fire, so try to reduce the number of turns as much as you can.
Another thing: Don't try to take too many defense boosts with you, only one defense boost can be triggered per turn (speaking of experience) and that one will be the highest max one.
Other recommendable medals:
Vexen B
HPO
anything with HP+800
Good luck!
First of all, let me say this: Just try often. I rebuilt setups from the Internet which failed to work for me because the fire attack WILL kill you no matter how much you turtle and the bomb attack might kill you or might not. I guess it doesn't have fixed damage but rather a damage range, so just keep trying. Dear thread viewers who have also beat the quest, feel free to share your solutions and comment so we can offer as many solutions as possible to make the quest beatable for as many people as possible.
My setup:
Fenrir Lvl. 31
HD Vanitas (put any copy medal here) - ATK Boost 5 - traits: def+2000 (dunno whether it made a difference)
Kairi EX - Second Chance 3 - no traits
HD Zexion - ATk4 Gauge 0 - strength+2000 and ground def, but doesn't do much damage anyway, so don't bother
Key Art Sky - defense boost 3 max - ground and Extra Attack
Warrior of Light - ATK Boost 5 Gauge 1 - no traits
HD Leon - ATK 5 Gauge 1 - +2000 strength
You WILL need defense boost 3 max. You don't need to use your EA 40 copy medal on Kex, use it on a turtle medal or strength reduction medal (in my case, Zexion). I used WoL and HD Leon here because they have the highest damage output of my medals right now due to the boosters, I guess everything's fine as long as it does damage. Ava might also be a good choice, I can't test it because I don't have her. The secret of the setup is that it doesn't waste a slot for a dispel medal - I tried a lot of setups with one that all failed because you can remove the status buffs he already did, but he will buff himself right before his attack so you can basically not defend yourself against that. Try to get a decent defense up and his attack down and try to deal around 500-600 bars of damage each round because you have to reduce the turns. He'll spit fire at his first turn and you won't survive that, you can't survive the fire, so you basically have to survive the bombs and hope that he doesn't attack you with fire more than twice. The problem with most all-turtle setups is that they drag out the fight for too long - the enemy has too many turns to buff himself up or maybe use the fire, so try to reduce the number of turns as much as you can.
Another thing: Don't try to take too many defense boosts with you, only one defense boost can be triggered per turn (speaking of experience) and that one will be the highest max one.
Other recommendable medals:
Vexen B
HPO
anything with HP+800
Good luck!