The last few “extreme” battle events haven’t been extreme at all. You can beat them easily with F2P friendly units.
To me this is the most obvious team. Cryogonal is probably not obvious to most people. Sinnoh doesn’t have good tanks so we abuse the Enduring effect from Brycen. This allows us to stay alive long enough to get 2 syncs in.
Grids on Blissey / Cryogonal are nice to have but not necessary. Blissey’s Master Healer helps a bit, and if you get MPR on Cryogonal you can survive even longer.