to be honest i'm not sure how much i'll practice in this event since i want to save as much seeds as possible for jack o latern event,
but i guess 2.5M PP shouldn't be a problem, so i'll leave the rest for my union members
ofc, it just about the seeds, i'll also use BP whenever i can so it's not like i'll stop to help them :O
anyway, as for the formation i'll go like that:

arc to cut damage, regeneration, attack debuff+ ambush as EX skill, so i'll go with A frame debuff while other member for B frame :O
svarog is kinda new, got her in that offense gacha, attack buff and damage
agni for fire attack boost
and amon to block sebuff, it say demon can block us from using skills, so if it's some kind of debuff i guess amon can block it.
and ofc brynhildr to heal and attack boost