Once inside the belly of the beast, you will notice again that the map in the world is incredibly small. You only need to gain access to one crown door, and there is only one boss battle.
Proceed in the direction of the special door, which is down one long corridor.
Boss Battle: Parasite Cage
Even with the acidic floor, Parasite Cage is just as easy as before, if not even easier. His moves are the same, as he slams his tentacles on your position, pushing the platforms under the acid for a brief time. Parasite Cage also buries its limbs in the acid, pulls out some acidic bubbles, and hurls them at your position.
Getting up close and hitting the oversized plant several times causes it to be stunned for a short periods of time, allowing you to use some powerful Sleights, such as Dark Firaga, which does some lethal damage.
After the fight, Riku levels up and obtains the Parasite Cage Card. Exit through the north of the map, using the save point before leaving. Riku finds himself back at Castle Oblivion, this time to face off against Vexen of the Organization.
Boss Battle: Vexen
Vexen is back to his pathetically weak self. Either that or Riku is just way too awesome for this guy to handle. Yes, Vexen still has his ridiculously large shield that he uses shamelessly. That being said, his moves are still very easy to dodge, and Vexen still leaves his back open for several seconds.
After the fight, Vexen tells Riku that their little skirmish was all a ruse to get battle data on Riku’s talents. Vexen disappears before the shocked Riku can finish him off. Now it is time to leave Castle Oblivion for Neverland.