This time, I just used the penultimate room of the game. Because the Altar of Naught is a "conversation pit" as I like to call them, just fall back in when you're close to losing Final Form and immediately head back.
This is a guide on how to level up Final Form.
For every completed Limit command, you will get 1 point toward your next level up. Rinse and repeat for the best possible leveling up method for Limit Form. (This is my own opinion on how to level up this form the fastest.
Once out of MP, go to the save point (before the form disappears) and leave the world. When you go back to the tower, your drive will be maxed out. When you're almost out of drive, rush back down the stairs and return to the Gummi Ship. Once you go back in, your Drive meter will be at max again. Repeat until you get Final Form. I only played KH2 so I dunno if it'll help you but I always used Valor when I could so I could level that up easy. I kept warping to the tower in Twilight Town, and just keep going up the stairs. From here on, after you get it, you may use Final Form like any other form, as it'll stay permanent. You can level up Final inside the Castle since alot of Nobodies spawn in there. How to Level Up Drive Forms Quickly A good way to level up Wisdom Form and Master Form quickly is at Timeless River in the four areas, Building Site, Lilliput, Scene of the Fire, and Mickey's House. Once you're in the tournament, use a form, and if it's not Final Form, quite the tournament, and you'll have full Drive Guage. Master form you can go to Mulan's World since the wooden crate thingies when … Also note that Anti-Form will never appear when you use Final Form. I always change up how I level Final Form. Keep repeating this until you are a Level 7. Wisdom you can level up in the Underworld or the areas outside the Castle that Never was (aka in the city) should you be that far. There may be other options.)