Muncey is Pete's dog, of an unidentifiable breed, in the 1953 animated short, The New Neighbor. He also appeared in the Mickey Mouse Works short, "Pluto vs. the Watchdog".
The New Neighbor
In The New Neighbour, Donald moves into a new neighborhood, finding that his new neighbour Pete, has a destructive dog, named Muncey. Pete gives Muncey a bone, to which he buries it in Donald's garden, much to Donald's dismay. Later, Donald gets another visit from Pete's dog who sends Donald a note for a favor, which Donald reads, giving enough time for Muncey to steal his dishes.
Donald goes angry until Pete visits again, to have him try what looks like porridge. Donald tries it and likes it at first but coughs it out upon realising that it was dog food (Pete had told the dog that he eats it). Pete then tell his dog he is too finicky, and this is the last time Muncey is seen in the short.
Pluto vs. the Watchdog
He appears in another short, Pluto vs. the Watchdog, where because of Pluto's ineptitude at being a watchdog, Mickey gets a new watchdog. Little does he realise the new dog is part of Pete's plot to rob Mickey's house.