Shy Guy Ghosts are undead Shy Guys that first appear in the game Luigi's Mansion. They can be red, yellow, green, purple, pink, white or orange with Shy Guy masks and are equipped with pitchforks resembling the one carried by Beezos from Super Mario Bros. 2 and the non-Mario game Yume Kojo: Doki Doki Panic. When Luigi uses the vacuum on them the masks come off revealing two yellow eyes in a dark void. Luigi can only suck up the ghosts once their mask has been removed. Shy Guy Ghosts have 20 HP, similar to Purple Punchers and a few Grabbing Ghosts.
- Mario vs. Donkey Kong has another same named enemy, they come in three different colors (red, blue and yellow like the Viruses from Dr. Mario) and if Mario pushes the button with the same color it transforms into a block (or a regular Shy Guy when fighting Donkey Kong). They only appear in the level Spooky House.
- Other similar enemies are Boo Guys and Phantom Guys from other Mario games.
- There were also going to be Blue and Turquoise Shy Guy ghosts in the final game but were removed for an unknown reason.