Arthur 3: The War of the Two Worlds (2010)

Maltazard, the Evil M, is now 7 feet tall and evolving among the humans, causing terror wherever he goes. His goal is simple: forming an army of giant henchmen and ruling over the universe. Meanwhile, Arthur is still a Minimoy, and thus in a state where hes unable to fend him off. With the help of Selenia and Betameche, he hatches a plan to regain his usual size: all they must do is infiltrate Arthurs house through the pipeworks, catch an electric train from his bedroom to his grandfathers study and find an elixir that will make him grow back to his human size. Sounds simple enough, if it werent for Darkos, Maltazards own son, hot on their tails.