Definitely a needed item, at least at some point.
I waited until like level 60 and got them when I spent a day getting my AF, which I got some sh*t over, lol.
Anyways, don't bother getting the key. It's such a bitch.
If you hit a monster that's behind the door, the monster will open the door when it comes to attack you.
Easiest way to target through the door:
Use Windower, and type //fillmode 1.
You'll be able to see through walls with this feature and there should definitely be something to pull through one of the doors with Dia/Ranged Attack within ~5min.
Don't try and do it without fillmode, will take too long. //fillmode 0 when you're done.
(Sorry if this is against the forum rules... definitely not detectable ingame however)
As for the fight, get a couple friends. Getting there is annoying, but if you get your pop item first, take control, lead, and open the door with the above method nobody should have a problem taking 20 min. to come help out.
I trio'd with MNK, DRG, and me on WHM. Not difficult at all.
Just a little info on the Mitts in case you don't know; eliminates half of Carbuncle's Avatar Perpetuation Cost. This means that with a couple of pieces you can make Carbuncle free - if you have a Refresh body (Yinyang Robe, Marduk's Jubbah, Vermillion Cloak) you can even get +1 MP/tick while Carbuncle is out. Very useful for soloing/kiting etc.
Especially if you're low on MP. You can just kite with Carbuncle and regain MP over time with the Refresh + Elemental Siphon (/Sublimation)
Edited, Jul 22nd 2009 8:20am by Poubelle