Marvin McNasty is the main antagonist for Pound Puppies and the Legend of Big Paw. He replaces Katrina Stoneheart's role as the Pound Puppies' archenemy.
Marvin McNasty is a short, rotund man who is approximately the same age as Katrina Stoneheart. He wears a purple shirt, purple pants, a purple coat, and black shoes. He also has a bald spot on his head and sharp teeth. He also wears a ring.
Marvin McNasty dreams of ruling the world. Marvin is sneaky, short-tempered, and doesn't tolerate stupidity. When he was reformed by his own Mean Machine, his personality is the opposite. He becomes a lot nicer and he helps out during the adoption bazar.
Marvin McNasty invents machines in his quest to rule the world. His Mean Machine can turn a kind-hearted person or an innocent puppy into a psychotic killer or a vicious guarddog.
- George Rose, who provided the voice of Marvin McNasty, was known for his role as Captain Janders in the 1966 film Hawaii, as Major General Stanley in the 1983 film, the Pirates of Penzance, and as Harold in the 1971 film, A New Leaf before he was murdered on May 5, 1988, which was only two months after Pound Puppies and the Legend of Big Paw was released. This is Rose's only voice role.