Main damage comes from Ventana.  However buffing her by supporters isn't enough, therefore you have to use mercs who can use incoming DMG boost or stats reduction.  That said, Ogdoad has stats weakening immunity, so normal incoming DMG boost or stats reduction skills do not work.  So you have to use...

First half, use mercs with decomposition skill, then use Endless Pain to extend duration.   One thing to keep in mind is that Ogdoad's AGI is 100% and that means debuff duration is cut down to half.  Second half, apply Concentrated Fire as many times as you can , then finish with Ventana. ★6 Ar...

First half, use mercs with decomposition skill, then use Endless Pain to extend duration.   One thing to keep in mind is that Ogdoad's AGI is 100% and that means debuff duration is cut down to half.  Second half, apply Concentrated Fire as many times as you can , then finish with Ventana. ★6 Ar...