I agree with Doomgaze, the Phoenix Cave and Kefka's tower are real good places to level up, while in the Fanatics tower, you cano only use magic, if I am right. And that is no funny thing. Cause there are a lot of storages to climb and when you come to the top and need to defeat the boss, you will see that you have run out of MP.

By the way, the Moogle Charm you can find at the place where Mog is standing when you find him in the World of Ruins.

I think Mog is one of the best characters in the game. When I found him he had an HP over 1000, while most of my characters at that moment weren't even close to the 1000.