This NM is not hard. I soloed him as a lv 70 drg/blm using a staff with uncapped skill, and I forgot to bring my AF helm, so I basically didn't use Healing Breath at all.
The NM if i remember correctly is a "Lost Soul" but is alot harder than the normal Lost Soul mobs you get scattered around Vanadiel. Soloed as 75 PLD/BLM (for warp) and from what i remember has a decent DEF as took me a bit of time to kill him. Hope that helps.
1) As a 40+ Corsair, go to Arrapago Reef and check the ??? you used for the Cor flag quest. 2) During the CS, the NPC will forget the name of the area where he saw the key item you need. He'll give you a cryptic description where you can choose either Maze of Shakrhami, Ordelle's Cave, or Gusgen Mines. (I think you can choose any of them but I did Maze of Shakrhami.) 3) At K-9 on the bottom floor (next to where Argus spawns), check the Iron Door to pop a Skeleton NM. I duo'd him as a 75 rdm with my NPC Pimy, it wasn't too hard but it started spamming Blood Saber (AoE Drain) at about 10%. 4) Check the Iron Door again for the key item. 5) Go back the the ??? in Arrapago Reef for another CS. Then go to the Shararat Teahouse in Whitegate and talk to Ratihb. Wait one real life day until midnight JST and talk to Ratihb again to get your Trump Gun.