She is probably the only sentient being Dan openly shows affection for, aside from Hortense,Becky, and very occasionally Chris.
She is shown to be quite intelligent as Dan managed to teach her various evacuation plans.
She also informed Elise's family their home was on fire.
Dan tends to feed her tacos before bed, which she is fond of. He also often feeds her turkey sandwiches and burgers.
Chris frequently brings up Mr. Mumbles as an example to Dan whenever Dan's willing to make himself disappear to fulfill vengeance on something annoying such as in Mall Santa and Family Cruise.
In Monster, Elise told Chris she'd rather shelter Mr. Mumbles over Dan. And she was shown taking the cat to bed and carrying her.
In The Catburglar, she seems to had made friend's with Honey's cat, Poopsie, in the ending.
When she gets scared, her first reaction is to claw Dan's face.
Whenever Dan is about to blame Mr. Mumbles for not helping him or doing something bad. She always lays on her back, roles around purring, and looking cute. In a few seconds Dan forgets her faults and instantly forgives her, while petting her tummy.
Dan would occasionally steal things for Mr. Mumbles (ex. in "Golf" He stole a 7 layer sardine cake for Mr. Mumbles' birthday.)
In "Art" she has a hatred for baths, and would claw Dan's back in the tub.
In some episodes, Dan would feed Mr. Mumbles human food. (ex. in "Catburglar" he gave her half of his turkey sandwich.)
Dan mentions in "Family Thanksgiving" that she is not mangy, "she's just not good at licking herself." After Don called Mr. Mumbles a "mangy furball."
She is a great listener and was trained even before she was adopted by Dan as she came back to Dan after the animals trampled him, Implying that she is loyal as all female cats are loyal to their owners.