The Parasite Cage is a Heartless summoned by Riku and Fagin to destroy the Shell Logue Squad and Sora inside Monstro.
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.
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.
Role in the Series
Like most other heartless summoned by Fagin, the Cage was very powerful to defeat, and it was only through luck did Spyro and Sora unite to defeat the creature. this heartless was intended to appear much earlier in the series, but offen ended up not making it's appearence, till the mentioned text.