So, I made what I think to be a very good team in PvP, and really any boss fight.
Raiou, Stormfox, Firequeen, Meowzard, Cherubion, Barricadus + the rest are attack-heavy arkadians.
Explanation and strategy: Leave Raiou Alone. Let it die, or alternatively “stun gift”, doesn’t matter. “Flash Bomb” with Stormfox really as soon as possible. “Offspring” with the Firequeen, and by now Meowzard should have arrived. Use meowzard’s “polymorph” on the offspring you summoned. Summon offspring with Firequeen. Use Polymorph on the offspring. Keep repeating the cycle until one of them dies, then go all out attack the rest of the way. The Cherubion is for healing the firequeen and Meowzard, and can be swapped for any decent healer. The Barricadus greatly helps survival of the FQ/MZ as the “Guardian” makes it so that basically only multi-enemy attacks hit firequeen/meowzard, which means less damage on them overall. I find this particularly useful as only the ones you want to keep alive stay alive, the rest (Raioh/Stormfox/Cherubion) die and give advantages. I find that I can summon at least 2 Extra 7*+ with this combo, and upwards of 8.
Hope this helps any of you struggling in PvP!