Catch and name a chocobo in the Chocobo Forest. Use Gysahl greens in battle to summon him! You can also move him to the Chocobo World mini-game (if you are playing on a Playstation, you will need a pocketstation, or if not just forget it). In the mini-game, getting the Mog's Armlet gives your GF the Mini-Mog ability. When used in battle Mog will partially restore the HP of all junctioned GFs. When he reaches level 50 he will evolve and become more powerful in his attack. Same thing at level 100.