Be at least lv60 and have the ultima wepon equip many hi potions and ethers and set reflet and cure and thunder as ur shortcut and have these abbilties euiped:
Scan
Guard
Once more
Mp rage
Leaf bracer
Damage drive
Combo boost X3
Air combo boost X2
Arial recovery
Retaliating slash
Slapshot
Upper slash
Horisontal slash
Finishing leap
Dodge slash
Slide Dash
Guard break
Explosion
Aerial spiral
Aerial finish
and get final form if u dont have it:
1: You must be on the World that Never Was, and have gotten past that event at Memorie's Skyscraper (Were you watch the cutscene when Sora has a keyblade war with Roxas on the "Dive to the heart" montage building from the beginning as Roxas).
2: Then you have the ability to become Final Form randomly, when ever you change into any form.(Kind of like Anti-Form)
3: Then travel to the Olympus Coliseum, and go into the underworld and enter the Cerberus cup.
4: Go right the split second you enter, turn into any form. If you turn into the form you chose, exit, and redo this step over and over until you turn into Final Form.
5: When you finally get Final Form, go to the world that never was and go to the Proof of existence room. Then go down the hall and go to the 1rst Hall of empty melodies and run past the nobodies, and enter the Naught's Skyway
6: Then turn into Final Form. Fight all of the nobodies, and when your drive gauge goes down to one, glide all the way back to the Proof of existence room, and go onto the save point, and exit to the world map. Yes. EXIT.
7: Then go back to the proof of existence room and do step 5 all over again until you level up six times. It is faster than it looks.
Hope it helps