Since it's pretty much imitating Vargas GGC, bring "Barfira" with you and put it up each round. That should water down the damage into much more tolerable levels. (also, replace Shiva)
Try and mitigate as much damage as possible on turn one. So the usual Full Break + Cheer(Embolden if you have it from Refia) and squeeze in Barfira where you can. Also, don't forget that Shiva is weak to fire, so either replace her with Siren(!) or equip anti fire gear. Other than that, heal on turn two and then proceed to layeth the smacketh down whilst maintaining your T1 buffs.
So if I bring Sustainer's absurd dude, and Full Break with Vaan, AND use Barfire, and try to chain paralyze with Chizuru I can win XD Think I need better armor
Barfira, Cheer/Embolden/Protectga, Full Break, etc. Basically, anything that can mitigate damage is what you should be using. CoD is one of the MVPs since she has Man Eater passives and has an all element resist ability. Use Shining Splendors if you have them; blind works wonders. It was reported on reddit that BC Lid's Hex Strike will always proc his susceptible ailments (possibly a bug).
3rd stage was difficult for me at first, but unlike some other super-hard in FFBE stages you CAN actually cheese it. Mostly because Vargas is human and he's vulnerable to status ailments. Here are some ways I've cleared it: 1) Cecil (heals) + Refia/Lenna/Tilith (backup healer, def down, cheer/embolden or Tilith's Celestial Light) + CoD (barrage). It's the longest and most painful way, but it's the bare minimum I've used to clear it. Chizuru + Diabolos is also not a bad damage dealer, but she gets outdone by CoD. 2) Maxed out Elza + CoD + Embolden/Cheer/Celestial Light can kill the boss in 2 turns. Use Elza to reduce Vargas' defenses by 50%, CoD barrage and after that spam Elza's 3 hit attack. Vargas goes down really fast. I've taken him down in 2 turns using this method. 3) Black Cat Lid trivializes this. I have absolutely no regrets pulling her during the Halloween event. Her Hex keeps Vargas paralyzed for pretty much the entire fight, her HP pool is decent enough that she's hard to kill when when he does attack and her DoT deals 55k damage a turn to Vargas, so even if you don't have CoD, he'll die eventually. Once I accumulated enough cacti to max her, I swapped Chizuru out for her. Since then I haven't lost a single fight. 4) When all else fails, you can do it the good old fashioned way. On the first turn, use Focus (for increased magic damage and better heals) + Cheer/Embolden (more attack and def against Vargas' attacks) + Deshell/Deprotect (depending on if your damage dealers are magic or attack based) + Power break/Fullbreak (to counter Vargas' attack buff) + Barfira (more mitigation) + Barrage (damage, use CoD if you have her). After that, focus on healing your units and killing Vargas as quickly as possible before the buffs/defbuffs wear off. Invoking Golem also helps a lot in mitigating damage.
My setup: Cecil, Refia, Karl, Tilith, CoD, Whatever friend (Elza/Luneth/CoD preferred) Turn 1 Barfira with Cecil, Attack break with Karl, Embolden, Barrage, Defense break Elza/Cut through Luneth/ Barrage CoD Turn 2 Heal with Refia, all out attack with the rest. Repeat step 2 if needed. If Refia gets taken out somehow, I just Heal with Cecil. Tilith is usually dead, just there for the bonus.
Yeah, Maxwell is tough, finally cleared it on my 5th try. Warrior of light, Refia, Agrias, Cecil, Cloud of Darkness, and Cloud of Darkness friend with Dual wield. Gotta keep Maxwell debuffed, your party buffed and fill the summon gage before you kill her so you can summon Diablos. On another note, I sent you a request on Exvius earlier in the week Hero/Nova. Name is Grifter, just like on BF. I'm going to change my lead to Refia I think, as my Cloud of darkness doesn't have dual wield, and Refia has dualcast. I tried to send a request to Sustainer as well but he's full at the moment.
I have no idea how everyone is so much further ahead then me... I play this game every day but I'm sooooo weak >_> anyway I got wiped in 2 turns by Maxwell with full 5's under full break, cheer up and the magic verIon of that... It takes so long to level even a single character I doubt I'll be able to get this challenge either