Kingdom Hearts II
After Maleficent resurrects Oogie Boogie, she leaves Lock, Shock, and Barrel behind to deal with Sora and Jack Skellington, and summons the Prison Keeper to assist them. It swallows the children to empower itself, but Sora, Donald, Goofy, and Jack manage to defeat it and release the children. With their usual disloyalty, they immediately reveal Maleficent's intentions to the heroes.
The Prison Keeper is a large, seemingly mechanical Heartless that seems to be made out of metal, and is thus predominantly shades of grey, black, and silver. Its large, egg-shaped head has a jagged, gaping maw and glowing eyes that are triangular spirals. Its face is not one uniform color, and seems to have been broken, as there is a crack between its eyes that appears to have been stitched or stapled back together. It has a long, twisted antenna sprouting out of the top of its head that appears to be wrapped in bandages. Its Heartless emblem is at the base of this antenna. Its long arms are connected to the bottom of its head, are mostly covered by metal "sleeves", and its hands seem to be made of bone. A large, metal cage holding the three children is suspended by a wire that hangs from the bottom of the Prison Keeper. The cage resembles the one that Lock, Shock, and Barrel use to travel Oogie's Manor in The Nightmare Before Christmas and Kingdom Hearts. There is a large, black knob on either side of the Heartless's head that seems to operate a the winch at the Prison Keeper's base.
In Kingdom Hearts II Final Mix, the Prison Keeper is brighter-colored, with a copper and gold cage, bright yellow hands, and turquoise arms.
The Prison Keeper's name refers to the cage it holds the three children in, which is reminiscent of a prison cell.
The Prison Keeper can imprison victims in its cage and swallow them to use elemental attacks. It uses Lock, Shock, and Barrel to help fight Sora's party. It can shoot large fireballs from its hands and blue lasers from its fingers. It also uses its claws and teeth for physical attacks.
Equip all of Sora's aerial abilities, and maybe the Hero's Crest. Also, equip Reflect to the shortcut menu. Fighting the Prison Keeper is all about maintaining pressure, so repeatedly assault it with air combos and limit attacks. If it tilts its head back approach it and use the "Inside Combo" Reaction Command to stun it. Valor Form is a good idea for this battle: Sora can obtain multiple hits to level it up all while keeping the pressure on the Heartless itself.
After a while it swallows one of the three, and its attacks depend on the child:
When reduced to 40% HP, it will swallow all three kids and use a mixture of attacks: fireballs from its eyes, slash attacks, and it will spin. Try not to go near it and instead use Wisdom Form, and continue attacking until it is defeated. Donald's Limit is also helpful here. If Sora runs out of MP, getting to the top of the Curly Hill may be the best way to start attacking the Heartless with the Keyblade.