From the Super Mario Wiki
Masterpiece is a downloadable microgame in WarioWare: D.I.Y. and WarioWare: D.I.Y. Showcase. It was released on December 9, 2009 in Japan, November 8, 2010 in North America, and December 10, 2010 in Europe.
At the start of the game, a boy is looking at the Mona Lisa. When he looks away by someone tapping his shoulder, it changes to a Charlie Brown-styled cartoon. The player must tap the painting to change it back to the Mona Lisa to win. It might take several taps for it to stay changed back.