The Mouse Agent is a small-sized agent has been seen in some episodes. In its first appearance, it's seen riding the elevator alongside the unnamed bear agent, unnamed crocodile agent, and others (" Isabella and the Temple of Sap"). It appeared again in " Phineas and Ferb Christmas Vacation!" dancing with the other agents. Its next appearance wouldn't be until , where it's seen attacking Normbots alongside its fellow agents. It had abs and bulky arm muscles. (" Phineas and Ferb The Movie: Across the 2nd Dimension Phineas and Ferb Save Summer ")
Its appearance is that of an ordinary mouse with a fedora.
Its boss in the
Agent M can team with the other Agents well, as it appears, in the 2nd Dimension movie. It is on good terms with Perry, and others, even its actual predators, so it can be assumed it does have friends in the Agency.