This when the Guardians discover that Lillian is the Heart of Earth and without Lillian knowing, Cornelia manages to transfer the Heart of Earth into Napoleon and bits off the Heart into Matt and Mister Huggles. This also formed the Three Regents of Earth. In "W is for Witch", Nerissa came back to Earth in order to get Napoleon on Halloween (the only time of day when a Heart can be taken by force.) Since Napoleon had most of the Heart of Earth's powers, Nerissa went on a wild chase to get him. Nerissa caught Napoleon who was really Phobos in a glamour (Unknown by Nerissa), after that, Phobos takes her Seal, and imprisons Nerissa inside of it.
In "Z is for Zenith" Napoleon helped Matt and Mr Huggles form a Glamour Zone round the Guardians and Lord Cedric to make no one notice and panic thinking a giant monster is coming to kill them. The plan worked and managed to take care of the Glamour Zone when Cedric was defeated. Most of the time, he spent most of his time with Lillian without telling her what Napoleon really does.
In the TV series Napoleon can talk and transform when he needs to as a regent of earth.
Originally, Will Vandom bought him from Matt's grandfather's pet store as a present to Cornelia Hale to help her to try and get over her heartbreak over Caleb. Cornelia gives Napoleon to Lillian. The girls first discover Napoleon can talk in the episode "U is for Undivided." Upon discovering that Lillian is the Heart of Earth, Matt and Cornelia convince Lillian to share her power with Matt Olsen, Napoleon and Mr. Huggles, making them the Regents of Earth.