Revisiting this as I finally geared my first toon in 9pcs Feral for the Demon Coalition Event (Venus). IIUC:
Against Demon Lord, If vneus has Dec Def, Weaken, 2 poisons & HPB out, that is 5 total debuffs, so as long as those are all up, every toon witll have a damage increase of 25%.
Against Hydra, if she has Dec Def, Wkn, & HPB on all Heads plus a couple of poisons out there, that would be 14 total debuffs. That should give a Damage Increase of 70% to the whole team?
Do I have all of that correct? I ran her on Hydra this week in the Feral gear (In place of Sicia) and did not really see much of a difference at all.