Dennis lives in his own little world, populated with various strange characters, friendly and otherwise …
The Opossum: Tucker once mistook the possum for his late sister Trouble the Kitty. Knowing a good thing when she saw it, the possum has been masquerading as a cat ever since. She is even more hostile to the dogs than Trouble was, but is not nearly as clever.
The mouse hitchhiked his way onto the Magic Flying Coaster when the dogs stopped at a cheese cave while on a world tour, and never left. A former NIMH experimental test subject, the mouse is quite possibly the smartest animal in the group.
Mr. Nibbles the guinea pig was hired by Dennis to be his life coach. Dennis certainly needs one.
Spicoli is a former DEA drug-sniffing dog who was involved in investigating Trouble the Kitty’s illegal catnip patch. Fired by the DEA for ordering too many pizzas, he now slouches around the house scarfing a seemingly never-ending supply of Doritos. How he obtains them is an open question, as is what, exactly, is his relationship to Rin Tin Tin.
Dennis’s frenemy Producer Smurf is constantly trying and failing to score big by selling Dennis’s stories to Hollywood, or whoever else may buy them. He also has a thing for pixies in general and Tinkerbell in particular.
Dennis’s nemeses are the ninja hedgehogs. They are generally responsible for all the evils in the world, up to and including Justin Bieber.
Cross the ninja hedgehog commander at your peril.
Sky Turtle is a semi-aggressive nomadic snapping turtle who floats in and out of the scene as the wind takes him. He is not a fan of mammals.
Whenever Dennis ends up in prison — which happens a lot — you can count on Bugs Bunny being his cellmate.