Just did this mission lastnight so I can give you a few tips on what to do. We went in as a pt of 6 rangeing from 59-71
Machtaru 62RDM/BLM
Me 61DRK/THF
Shadowblade 60PLD/WAR
Sxdigital 71RNG/NIN
Dealtaru 60WHM/SMN
Ashelus 59BLM/WHM
We went in through the keep all sneaked and invis except the rng no aggro there. I highly recomend 1). some one who knows the way there and 2). a person high enough to walk through the entire area with out getting aggro. This helps out because the doors you have to open have mobs such as goblins that agrro to sight. Since we had some one who didnt catch aggro, we didnt have to drop invis to open the doors, we just had the rng do that for us. Went in past the keep into the throne room and got some freak'n awsome pics. Once we made it there we buffed up eating bob's and pie ect. Went in and had to wait for every one to finish the cutscene before we could begin. 1st form is by far the hardest, just all meelee no magic can hurt him. After you take him down to roughly 50% health he becomes imune to physical attacks so make sure you donot blow your tp at this point just all out nuke. After the first form you have to fight him in the 2nd form. This is when we went all out on him because all he does is an AOE attack no there is no need for a tank at this point. Guillotine 990, Slug Shot, 1134, Skillchain Fragmentation 344, Eagle Eye Shot 998, and a few more nukes and he was dead.
Hope this helps, have any questions on strat just send me a tell ingame I'd be more than happy to fill you in on the details.