Paper Mario World
How to Play: L/R Arrow: Move - Up Arrow: Jump - Space: Hammer
Paper Mario World has a unique plot in which Princess Peach has been kidnapped by the evil, plotting, S.O.B. Bowser... oh wait that's actually not unique at all. The unique part about this flash game though is that you play as Baby Mario and get to wield a Hammer that smashes the living snot out of all your typical Mario enemies like Goombas and Turtles and what have you. Pretty sweet deal if you ask me.