Shadow Mario

From Mariopedia

Shadow Mario is just Bowser junior in disguise. Mario got accused for vandalism, due to Shadow Mario using the E.gadd paintbrush to spread the "sludge" all over delfino isle. He is seen in almost every level, and in the levels he is in, Mario has to chase him. In pinna park, Shadow Mario reveals himself, showing that he is Bowser junior. In the airplane cutscene, Princess peach sees him running in the background of the delfino intro.