Gus is one of the secret characters that can be unlocked in the Haunted Mansion section of Disney Crossy Road! In order to unlock him, all you have to do is unlock the 'Spooky Spirits' set of characters. These characters include Prof. Phineas Plump, Madame Leota and Executioner. Once you unlock these characters (in no particular order) you will unlock Gus!
If you know how to unlock any other Disney Crossy Road Secret Characters, make sure to tell us in the comments below!