The Parasite Cage was a Heartless sent into Monstro to find and capture the heart of Pinocchio (and possibly locate Monstro's). It captured the puppet when he ran away from Riku. However, before it could succeed in escaping, Riku, Sora, Donald, and Goofy battled it in Monstro's Bowels. Eventually the Parasite Cage spit out Pinocchio and climbed away into Monstro's depths. Despite being defeated, the Parasite Cage retained Pinocchio's heart.
Sora chased Riku into the Stomach, only to discover that the Parasite Cage had lodged itself there. With Pinocchio's heart, the Parasite Cage had increased in size, and had become much more powerful. Sora battled it one last time before it was finally destroyed.
Kingdom Hearts: Chain of Memories
Parasite Cage is seen in Castle Oblivion as a figment of Sora's memory in his memories of Monstro. It captures Pinocchio when he tries to escape from the danger that was coming. Sora then fights the Heartless until he manages to knock it out. After Sora convinces Pinocchio to act brave, Pinocchio fights his way out of the Heartless until he escapes. After the Heartless disappears, Pinocchio reveals that the monster spat out when he started fighting back and that Sora and his friends should try that on Monstro to help him and Geppetto escape.
The Parasite Cage also appears to Riku, as a figment of his memory and a representation of the darkness within him.
The Parasite Cage's main body is a large, magenta blob with glowing yellow eyes and thin, rounded teeth that resemble prison bars. This body rests on a flower-like base that is violet and aquamarine. A much smaller pink head rests on top of the main one. This second head sports a jagged mouth, glowing yellow eyes, two short, dark purple spikes under its mouth, and a curled, magenta antenna on its head. Two long, aquamarine tentacles sprout from either side of the second head and end in violet "hands" with three fingers, each with a dark purple spike on it. Its Heartless emblem is between its eyes.
In Kingdom Hearts Final Mix, The Parasite Cage's main body is light orange, as is the antenna on the smaller head. The smaller head is light tan and the small spikes on it and its hands are blue. Its arms and base are pale green, its hands are yellow, and the flower-like section of the base is violet and lavender.
The Parasite Cage's name reflects its apparent great appetite and the fact that it is fought inside another living creature. "Cage" clearly references its mouth, which resemble prison cell bars, and its ability to capture opponents. Its appearance is also similar to the Prison Cage from Final Fantasy IX.
The Parasite Cage mainly uses its tentacles to attack opponents. It attacks by swinging them or slamming them on the ground. It can trap enemies in the mouth on its body. It can also suck Monstro's stomach acid through its tentacles and spit it out through the top head.
At the start, remain on the platform and lock on to the Cage's head, shooting Fira or Gravity spells at it. Keep doing this until it's beaten and escapes. If Sora needs to recharge, either use an Ether or attack the head and cage with the Keyblade until he's regained enough MP. Riku will aid Sora in this battle, making him the only fellow fighter in the battle. After winning, Goofy learns the Cheer ability. Note that if Neverland is completed first, Riku will not appear and will not be there to help.
This fight is much the same as the last one, but the Cage has developed a new poison breath attack. When the Cage gets tired and sags backward for a moment, its mouth will open. Bash it with the Keyblade and try to execute a couple of flying combos during this time. When it recovers, return to the normal strategy of casting spells at the head. Eventually, it reverts to its old strategy, and Sora can get closer to smash it with the Keyblade. Be careful not to step in the green acid surround the field, as it will damage Sora. After the battle is over, Sora and Donald will learn the Stop spell. The party is then automatically ejected from Monstro and returns to the Gummi Ship.
Kingdom Hearts Re:Chain of Memories
In both Sora's and Riku's battles with the Parasite Cage, there will be four revolving platforms, floating on digestive acids. Using the Gimmick Card will cause these four platforms to disappear, and a large one to appear in the center, close to the Parasite Cage. Avoid stepping in the green acid as it will deal damage to Sora/Riku.
Since Riku obtains the Monstro world card within the first few stages of the game, defeating the Parasite Cage is simple. The only thing Riku needs to do is successfully fill the Dark Points gauge bar up to 30 by breaking every single card. After that, attack the Parasite Cage—simple attacks, sleights, or anything else. Note that while Riku is in Dark Mode, HP orbs come out of the Parasite Cage with every attack, so it is easy to heal and stun the enemy. In addition, Riku has the Search Ghost enemy card to heal him each time he strikes it.
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