NIN/RNG with a excellent fire resist set, and tons of Shurikens or a ranged weapon + RDM/WHM can duo it, pretty sure 2 is the lowest you'll be able to win with.
I was able to dual box it NIN/RNG + RDM/WHM, but was very very close on time.
This is the fire resist set I used:
minus the flame sachet for a RA weapon when it starts to fly, and I used Neptune's Staff. M.Eva Sekka+2x2 would be better... they're just stupid hard to get.
I had my RDM mule stay really far back and tail tanked it while it was on the ground to avoid terror, you just need to keep up with shadows, but at 90 it shouldn't be any issue at all.
When it starts to fly have the RDM throw DoTs on and start dealing as much DMG as you can on NIN with Ranged attacks/Barrage/Sange, or a Futae nuke here and there with nuke set. Have the RDM throw out nukes while trying to not pull hate off of the NIN. With my set and barfira I never really got hit for more than 20DMG.