I was able to solo tank this with slightly above average PLD/NIN Gear (That means HASTE, not HUR HUR DEFENSE AND VIT).
Set up was, PLD/NIN, RDM, WHM, BRD, BLU, SMN.
BLU/THF was good for a SA/Cannonball which is effective at dealing a good deal of Damage with limited TP feeding. Theres plenty of better set ups in terms of killing quicker im sure, and most parties will require two tanks if your party is inexperienced with anything higher than greater colibri.
Took about a good 20-30 minutes all-in-all but never got close to dying a single time and was very fun. good idea to disengage during Ice/Fire mode as the spikes damage/paralyze is annoying.
PLD/NIN and NIN/DRK both apparently work for this NM, but it spams Aga-Spells often and can cast -aga debuffs so NINs will find themselves lacking shadows are critical moments at times, but a good one can recover and both work.
Oupire is soloable with some luck by a BST90 using Dipper Yuly.
My strategy was:
Call Beast > Wait for recast. Use a Zoolater's Hat charge, while keeping Glyph Axe on. Then toss your pet on him and watch.
After various kills I noticed that the most annoying thing with Oupire is his spells, because apart from that, he's not really damaging your highly evasive pet. Since I wasn't meleeing due to annoying AoE spells and WS, I decided to come /blm to stun and it worked great. Dipper was highly resistant to wind and earth based spells, and I would only stun other spells and wipe his Utsusemi after Wings of Gehenna with Poisonga(beware the surrounding monsters). Frequently, your Stun wouldn't be up and he'd cast a big spell that'd hurt your pet. In this case I'd WS with Sudden Lunge.
The only thing that can be annoying is if Oupire uses two unresisted Eternal Damnations back to back, like, when your Call Beast timer isn't ready. You can be lucky if he doesn't use Ice mode at all.