If you search for Nintendo or Nintendo related things such as systems or characters, you'll find greyed out entries that produce the coin sound from the mario games when selected.
Play Manhole
While in the universal dictionary mode, search for "MANHOLE" and select the greyed out entry that appears. You'll be able to play the old Game&Watch game on your DS!
Play more Game and Watch games
Choose all dictionaries (lowest entry on the upper left - "green") and enter the following in order to play the respective titles: