If you want hints for the final parts of the game, here's a few:
- You can run away from the bosses in the crystal floors by using Edge's Smoke ability. This works even against Zemus' Breath and Zemus' Mind.
- Don't worry about spending a lot of MP on the crystal floors, you'll be fully restored just before the final battle.
- During the final battle, have Rosa use Cure4 on every turn. Be careful when using spells against Zeromus because he'll often counter them. Have Kain jump and Edge throw weapons.
- Lowering the battle speed will make the battle considerably easier (Zeromus will cast 1-2 Big Bangs every turn on the fastest speed, but on the normal speed, he'll cast a Big Bang every two turns or so).