Go to narshe and recruit Mog. After doing so go to the northernmost part of town, the area where you obtained tritoch/valgarmadia and hit A right at the end of the cliff where it was sitting. A message will pop up saying you have found a secret area will pop up (make sure you have mog in your party before progressing). You will find yourself in a dungeon, at the end, you gain "Midgarsomar" or something like that magicite and you fight a yeti. If you win, after the battle Mog will berate him and he will join the party.