In the Ballroom, the Shy Guy Ghost can only be sucked up when Luigi sucks up its mask. It reveals a pair of yellow eyes with a dark void.
Fire can help beat the Shy Guy Ghosts quickly by firing at them.
Shy Guy Ghosts are found only in the Roof, the Ballroom and Astral Hall.
Shy Guy Ghost (Nintendo DS)
There's a new enemy with the same name that apppeared in Mario vs. Donkey Kong and come only in a trio of colors, like the Viruses and if Mario pushes the button, it turns into a block or a Shy Guy. They are found only in the level, Spooky House.