After clearing the room of Heartless, use the north door and synthesize using a card with a value of 1 or more. Do the same for the following rooms, except use different doors. In Room 2, use the left door. In Room 3, use the north door. In Room 4, use the north door. In Room 5, use the left door. In Room 6, use the south door. In Room 7, use the left door. In Room 8, use the south door. In Room 9, use left door (also synthesize using the Key of Beginnings) and you'll come face to face with the boss.
Oogie Boogie is all about dodging and Card Breaking. From where you start, a gate will be in between you and Oogie Boogie. Since you don't have the option to attack him, you'll have to card break the dice he throws down. Once that's done, the gate will lower and Oogie Boogie will throw more dice down. Keep repeating the same process and eventually the gate will lower completely. Attack Oogie Boogie with your best cards until the gate comes back up and your way is blocked once again. You'll have to card break more dice before you can begin to attack him again. Oogie Boogie isn't too tough a boss, his attacks including:
- A rotating saw blade goes around the arena. Dodge this the best you can with a dodge roll.
- Another blade attack where two blades are being smashed all over the arena. Once again, use the dodge roll to your advantage.
- Oogie Boogie brings random Heartless into the arena to attack Riku. Fight them like you would any other Heartless.
Additionally, Oogie Boogie can heal himself, sometimes making it time-consuming to actually defeat him. Once you do defeat him, use the north door and enter Room 8. Use the right door to go back to Room 7. Use the north door to get back to Room 6. Use the right door to get back to Room 5. Use the north door to get to Room 10. Use the north door to return to Castle Oblivion.