I was in a party heading to the Windurst Walls entrance/exit of Toraimarai Canal to skillup, and we stopped off to see this guy. Party:
70PLD/WAR
72WHM/BLM
70SAM/THF (he was just subbing it for skillup, no TA)
62WAR/THF (Only had GA, which he was skilling up)
60RDM/BLM (Me)
So we start physically attacking him, I Gravity, Paralyze, Slow, and Dia 2. I tried to blind but, as previously mentioned, it doesn't stick. We /poked him for about 5 minutes, got him down to half health, and suddenly he used Mighty Strikes. I landed a Gravity, and the PLD, WAR, and SAM all ran to the other side of his room. At this point Oni Carcass pretty much stopped moving, or moved really slowly. We waited for a while, then went back.
/poked him some more, killed him, and got undead skin and dark crystal, but we were generally happy with our fight. VIT down isn't fun for tanks, so I recommend Erase. It is possible to kill this guy physically, and his INT down attack makes me recommend it.