Stealth Sneak

A giant chameleon-like Heartless It's capable of turning invisible, and therefore rather sneaky. The Stealth Sneak was sent to find the keyhole in the Deep Jungle. It corrupted the heart of Clayton, and used him like a puppet until it died after toppling on Clayton, crushing him to death.

The Stealth Sneak bears a resemblance to the Illuminator from Kingdom Hearts II.

Journal Entry
''Heartless that attuned to the darkness in Clayton's heart. It somehow manipulated the light to turn invisible and fought alongside Clayton.''

Kingdom Hearts
In its first appearance, you will be facing the Stealth Sneak with Clayton as its rider. It is best if you focus on attacking this creature first, depleting its first HP meter to render it visible. The Stealth Sneak then acts a lot like Sabor. Continuously attacking it and using Fire spells will do lots of damage. During the first part of the battle, you can also use Thunder spells to strike at both Clayton and the Stealth Sneak simultaneously. Three of these creatures appear later during the Hades Cup, but without riders and with a new dark-gray coloring.

It has two main attacks, a lunge and a "spell" of sorts. The lunge can be dodged by Dodge Roll. When visible, the attack can be seen by the stance it takes before lunging, but when invisible, the best when to "see it coming" is by locking on to it, since the stance involves it lowering the head, which is the thing that Sora locks on to. So when the Lock-on ring suddenly lowers, dodge. Its other attack can be seen either way. Its hands start glowing and it will extend them, and when it brings them together, the attack launches. Simply time a jump with the movements of its arms.

Trivia

 * There seems to be some confusion on how the Sneak killed Clayton. When the Disney villains are discussing it, Oogie says he "got chomped", and indeed, if one looks closely, it does appear Clayton got crushed in the Sneak's open jaws as it fell on top of him. The cut scene is not clear enough to make out all the details though.
 * In Kingdom Hearts: Final Mix, the Stealth Sneak was redesigned with stripes to give it a more Heartless look.