He is the Funky Phantom's pet. Boo is a white ghost cat who wears a hat with a red feather in it. Before becoming a ghost, Boo was a brown cat with a blue hat.
Boo is rather cute, a bit cowardly (though not as much as his master), and also very mischievous. He is often found teasing Augie's dog, Elmo, who is always pursuing him. Despite their feuding, Boo is willing to help the persistent bulldog whenever he's in trouble as shown in episodes "We Saw a Sea Serpent" and "The Hairy Scarey Houndman". Like Elmo is with Augie, Boo is very loyal to Mudsy and aids him whenever necessary.