Keith

Keith is the monster in the sixty-first Goosebumps book, I Live in Your Basement!

He was a monster with the ability to warp realities and transform into anything. Keith's goal was to make Marco his slave,. But in the end, it turns out he is a normal human-like monster who wishes not to be seen by Marco

Appearance
Keith looked like a yellow blob of human organs connected by webs of purple veins in his dream, but really looks like a normal boy.

Powers
He had the power to go into Marco's dreams and change his mind.

Trivia

 * Keith is one of the blobs (King Jellyjam and The Blob Monster).
 * Keith is not a child (as believed).
 * Keith is one of the villains who didn't fail.