You get the order of killing this monster from Montblanc himself. After accepting the hunt you won't have to search for him for too long. He'll ask whether you want to hear the details or not. Mondid will help you with this assignment once again, but he doesn't seem to be happy with that fact.
Belito should prowl in an isolated area in Nam-Yensa Sandsea. To get there you'll have to go to Zertinan Cavers from Ogir-Yensa Sandsea (using the most western entrance). When you reach Nam-Yensa go upstairs and to the most advanced platform. There Mondid will await you. It turns out that this hunt was just a provocation. The real target is Ba'Gamnan and despite all appearances Mondid doesn't work with him. His task, on Montblanc's order, was to draw you out to lure Ba'Gamnan.
About 118 000 HP,
About 28 000 HP,
About 24 000 HP,
About 26 000 HP
Resistant to Libra,
Vulnerable to Water (all of them)
At the whole beginning of the battle it's best to take care of Ba'gamnan's henchmen first. They're weak so you should deal with them fast and focus on the main dish.
He doesn't have especially varied list of attacks. Beside the normal attack, Kick and Lunge he uses Shining Ray which deals Holy damage to everyone in range, but you can deal with this easily by equipping White Mask or Sage's Ring. The enemy also knows how to use Eviscerator, which deals everyone in front of him.
Bounty (you get it from Mondid): 5100 gil, Magalixir.