Yikk

Yikk is a character in Mario & Luigi: Bowser's Inside Story who owns the Tower of Yikk and is also found inside of it. When Bowser enters the Tower of Yikk, he will find a book on a table on the top floor of the Tower of Yikk containing Yikk. After that, the entrance to the room is blocked and Yikk reveals himself to Bowser and shows him the Boo-ray Machine that he created. He states that he uses it to study Boos and other ghost-like creatures. After explaining on how to use it, he goes back into his book and shuts it.

Trivia

 * Yikk is possibly related to Professor E. Gadd, due to both of them studying ghosts.