Barthandelus down. Team looked like this:
Cloud - Blizzara Strike, Retaliate, +Knife damage RM (he had Keepsake Knife equipped)
Lightning - Tempo Flurry, Thundara Strike, Self Sacrifice
Fang - Tempo Flurry, Thunder Jump, Attunement II
Y'shtola - Haste, Protectga, Mako Might (SS2)
Lenna - Curaga, Shellga, Dr Mog's Teachings (Princess's Favor)
RW Advance
Notable RS gear was a Keepsake Knife on the Retaliate, the freebie gun on Lightning, and various bangles on the three fighters. Fang carried my max augmented Brave Blade++ since I didn't have a good RS weapon for her, the healers had Regal Gowns and Giant's Rings for durability.
It took me six tries to get the timing of when to use SS2 right. Do it too soon, and it'll fall off right when the Pauldrons are getting nasty; do it too late, and risk getting offed by focused fire. Barthandelus himself was much less threatening with SS2 + Protectga + Shellga + AoE heal on my side; the first time I got to him, I won.