Originally Posted by
Kureru
I can answer for fire at least. Fire debuffs generally won't stack with each other, the exceptions being Raguel's attack down, Hephaestus' def down and Mars' resistance down. Note that Hephaestus and Mars aren't released yet.
A team of Amaterasu, Svarog, Kagutsuchi, Brynhildr is very strong. Use ambush to reach 40% def down (soul ex skill).
The exciting awakenings for fire are Svarog and Uriel. Before awakening Uriel probably loses to Kagutsuchi but you may want to try her.