Nintendo Super Mario Bros. Ghost Boo Plush Boo! Maybe he's related to a certain British rock singer. The spectral Boo is a limited availability Ghost Plush Doll. Complete with beady eyes, long tongue, and sharp fangs! Boo! Maybe he's related to a famous rock singer. From the Super Mario Plush Series, this official Super Mario Plush Doll spotlights the spectral Boo as a limited availability, 5-inch tall Ghost Plush complete with beady eyes, long tongue, and sharp fangs. Could he pass for a member of a certain British rock group? Boos (or Ghosts) are spectral beings with beady eyes, long tongues, and sharp fangs. The first appearance of Boos was in Super Mario Bros. 3, where they appear under the name 'Boo Diddly,' a pun of musician Bo Diddley. In Super Mario World, there are much larger variations of the Boo under the name of 'Big Boo.' All Boos are ghostly creatures that are able to pass through solid matter.