managed to beat them all on standard, stats around 75-80ish on everyone(except the protagonist who was all 90s, and Masakados who was 80-90)

primer in case anyone else is dumb enough to try fighting these buttholes

Belilal
-Butthole
-Shifts weaknesses whenever his is hit, starts weak to ice. Will never be weak to fire.
-Uses chiefly physical attacks with the occasional Trisagion and Mamudoon thrown in, making him actually the easiest of the bunch by far
-Knows Dawn's Chariot, a random-hit physical move that hits super hard and ignores all physical resistances/drain/reflects. He doesn't use it that often but someone might die when he does.
-When he hits half-health he'll start using Tyrant's Eye, which skips his current turn and gives him 2 actions on the next. If he decided to use a double Dawn's Chariot then you're about to have a bad time.
-Will instakill the entire party with a move called Doomsday after a certain amount of turns, his timer seems a bit tighter than the others due to his simplicity
-No punishment for buffing/debuffing, so go nuts.

Just hit his weaknesses and you'll be fine, the only real challenge here is doing enough damage quickly enough. His magic stat isn't great so even neutral buffed spells will hurt him.

Rewards you with the Lucifer Sword, an 180 attack sword with Pierce

Nebiros
-Total butthole
-Shifts weaknesses whenever his is hit, always starts weak to gun. Will never be weak to ice.
-Anyone who attacks him physically is immediately killed, even if they miss.
-Knows Calamity Cycle, an ability much like MA's Disaster Cycle, it's an almighty attacks that hits the whole party and gives out random statuses, except it hits like 10x harder than the original. Spams the fuck out of this. Brave Heart is a must if you don't want to be constantly on damage control.
-Occasionally throws in a Mabufudyne which hits even harder than Disaster Cycle, it's still more manageable though.
-Will very rarely just waste turns on Strike and Mamudoon
-When he hits half-health he'll start using Zero Morality, which is Asura Roga on steroids. Remember that if an Enraged character attacks him he will still instakill them. Brave Heart is again your only real defense here.
-Will instakill the entire party with Doomsday after a certain amount of turns
-No punishment for buffing/debuffing, so go nuts.

Again, target his weaknesses and get ready to res whoever draws the short straw and has to punch him. Because of his instakill defense his actual defense stat is hilariously low, and he will be absolutely shredded by a Charged Fleeting Rain at max buffs/debuffs if you use Spearhead beforehand or he's weak to Gun again. Amped non-ice elements are also good.

Rewards you with the Lucifer Gun, a 160-attack gun with the Final Seven skill which does heavy gun damage and has a 100% crit rate

Lucifuge
-A massive butthole.
-Shifts weaknesses whenever his is hit, starts weak to Elec. Will never be weak to Gun.
-Has a fucking insane magic stat and will just straight-up murder your dudes one-by-one with basic Dyne spells that hit for like 2000 damage if you don't resist them.
-Is Strong to everything he isn't weak to, but is rather flimsy HP-wise so it's recommended to fish for his weaknesses.
-Starts using Concentrate early in the fight to kill things extra-hard
-If you try to Makarakarn him he will just start throwing out Big Bangs and murdering everyone.
-If you try to get cute using Spearhead he will Concentrate + Big Bang you, almost assuredly killing everyone. He does this in response to basically any shenanigans whatsoever, and sometimes just when he feels like it.
-Will instakill the entire party with Doomsday after a certain amount of turns
-No punishment for buffing/debuffing, so go nuts.

A short-but-deadly fight, it's more-or-less a damage race. Debuff the shit out of him ASAP and fish for his weakness, throw in a couple Luster Candies too. If you luck out and he shifts his weakness to Phys then go all-in. Make absolutely sure you're full on summon stones and that everyone has some kind of Endure skill. Spearhead + Charged Fleeting Rain makes for a good finisher when he gets low enough.

Rewards you with the Lucifer Ring, which makes you immune to all ailments.

Beelzebub
-King Butthole of Butthole Mountain
-Has no weaknesses whatsoever and sky-high magic defense, but takes good damage from Gun.
-Is fast as hell and hard to hit with anything unbuffed
-Will immediately instakill the entire party with Doomsday if he is debuffed at all so uh don't do that
-Will immediately Dekaja if you hit +4
-Loves to use Tetrakarn and Makarakarn to completely fuck up any offense you're mounting. There is absolutely no pattern to this so you'll just have to deal with your gunner blasting themself in the face for 3000 damage and dying sometimes.
-Will sometimes throw out a Grand Piercer or Beserker God at the protagonist, will probably succeed in one-shotting him if he doesn't resist phys/gun.
-Has a complete dick move that immediately drops everyone to 1HP and has a high chance of Poisoning them, so if he goes first and you don't get off a Salvation then multiple people are definitely going to die. Brave Heart or Void Nerve is the only way to not get devastated from this unless you're very lucky.
-Will throw out Antichithons sometimes, if you're buffed at all then this is negligible.
-If you've been especially good this year then the spirit of Christmas will enter your game and make him waste a turn on Mamudoon.
-Knows both Dawn Chariot and Calamity Cycle, because fuck you. Rarely uses either but will almost always ruin your day if he does.
-Knows Diarahan and will use it when on his last couple-thousand HP, because fuck you. If he does this then you lose, because
-Has a time limit like everyone else

This guy is an absolute shitter. Charge + Fleeting Rain will deal good damage if you can hit him at all, make sure you know the turn order of your dudes in case you get poisoned, make absolutely sure whoever is going after him casts Salvation every single turn unless Brave Heart is active. Finishing him off is down to luck, once he hits red health it's not long to go until he Diarahans so make as big a ball of burst damage as you can. I killed him thanks to a lucky Blitzkreig giving me an extra round to beat him up before he healed.

Rewards you with the Lucifer Vest, a 140 def armor which nulls Curse and is strong against all elements

doing all this bullshit gets you a crappy app that reveals the entire map, whoopee. thanks lucy