must have:
-buff potion
-healing potion
-1 pull/swap hero (ninja,warlord,zealot,king maleos) i use ninja
-1 4*+2 Seraphina (ally) get the best u can.
-2 or more DPS
-'Enuff HP' *
Arrange your team accordingly by taking advantage Seraphina ally aura direction
use 1 weakest hero so Seraphinas ally can replace asap. put your puller/swap-er hero in the middle for best output.
Stage 1:
replace your weak hero with Seraphinas ally asap. by 2nd rounds it clear
stage 2: (the annoying cheating chest)
DO NOT ATTACK. JUST KEEP END TURN untill it explode
DO NOT USE ANY SKILL/SHIELD/HEAL. just take the damage. *this is why must have enuff HP cost i dunno the explosion cause by attack or magic.
Note: reason using this method to make sure all 4 chest to explode at once. trigger any attack/skill would delaying the explosion. thus, take many round just in this stage.
stage 3:
heal - buff -swap/pull - kill
btw my team gladiator,ninja,Lucille,cybella & 1 weak hero. only use skill swap n heal the rest normal atk.
thats it:

credit: Tyrias & all Seraphina fella out there.
p/s: sorry for my bad grammar/etc lol