Mr. Fuzzums is Dee Dee's beloved stuffed bear.
When Dee Dee tries to get Dexter to play with her, Dexter is annoyed by this and pretends to play with Dee Dee, only for her to watch as the space training machine (Dexter caused it to malfunction) shoots Mr. Fuzzums out onto the curb, be taken away by a garbage man and thrown into the city dump. Dee Dee goes insane when this happens and Dexter realizes his mistake and goes to the dump to help Dee Dee find Mr. Fuzzums successfully. Mr. Fuzzums also appears to actually be real. For example, when Mr. Fuzzums is in the garbage truck, he stares at Dee Dee as he goes to the city dump. He may be Dee Dee's second favorite toy (her first favorite being the line of Pony Puff Princess) because when she lost him she was deeply depressed.
Dee Dee has cookies and milk with her stuffed animals, and Mr. Fuzzums is one of them.