Cheshire Cat

The Cheshire Cat is a pink and purple cat from Wonderland with mysterious powers and constantly teleports from one place to another. He speaks in riddles and wears an almost permanent grin on his face.

Kingdom Hearts
In the first game, this cat aided Sora at first, but then turned against him by summoning the Trickmaster, which the cat called "Shadow", but after defeating it the Chesire Cat reveals to them that Alice was taken away by the Heartless into the shadows. It was revealed in the Manga that the prank playing cat was working for Maleficent but betrayed her when he gave Sora the ability to use Blizzard magic to destroy the Trickmaster.

Chain of Memories
The Cheshire Cat appeared in here as one of Sora's Wonderland memories, giving him advice on how to save himself from being executed by the Queen of Hearts (albeit in riddles).

Quotes

 * "Shadows here, shadows there, shadows everywhere, and the mome raths outgrabe!"
 * "The shadows are coming! Are you prepared for the worst? If not, too bad!"