Mr Mumbles - Barry Hutchison (Invisible friends #1)

Goodreads 3.96

Kyle’s imaginary friend from childhood is back… with a vengeance.

Kyle hasn't seen Mr Mumbles in years. And there's a good reason for that: Mr Mumbles doesn't exist.

But now Kyle's imaginary friend is back, and Kyle doesn't have time to worry about why. Only one thing matters: staying alive…

A major series from a fresh new talent, brought to you by the publisher that put horror on the map