Yikk is a character in Mario & Luigi: Bowser's Inside Story.
He is a ghost who invented the Tower of Yikk and the Boo-ray Machine. When Bowser encounters him in the Tower of Yikk, he appears from a book that Bowser is reading. He created the Boo-ray Machine to study ghosts, so he is similar to Professor E. Gadd in this aspect. Yikk explains his machine and how to use it, but then he goes back into his slumber.
- The Prima Guide doesn't call him by his actual name rather just calls him the inventor.