Be careful at the Tower of Fanatics. I recommend that you bring Mog and Equip him with the Moogle Charm there, as the enemies can get really tough. The monsters there are in lvl's:10,20,30,40,50,60,70,70,80, and 90. You don't want to fight the higher ones, because I'd assume you are probably less than lvl 50. They really are tough.

You could also fight the White Dragon in the Tower of Fanatics. This battle can be a little difficult because you are restricted to only magic and the White Dragon can also cast Holy about 3 times in a row.

And finally, once you take the Gem Box (that lets you cast two spells per turn), you will fight the boss, the MagiMaster. The MagiMaster has the annoying ability of WallChange, and since you are not allowed to use physical attacks, you either have to guess his weakness, or use non-elemental magic such as Flare, Meteor, and Ultima. Now, the most important thing of all is that once it's HP reaches 0, it will use Ultima as a final attack.

There are four ways to surivive this:
1. Pray that you have enough HP to survive (Good Luck)
2. Cast Life3 on a character before Ultima.
3. Use the Palidor Esper, which causes all your characters to use Jump. But you must be able to kill MagiMaster before the final Jump!
4. Rasp all it's MP. I think it's probably 50000 or so.