From the Super Mario Wiki
A Shy Guy Ghost
from Luigi's Mansion
Shy Guy Ghosts are undead Shy Guys that appear in the game Luigi's Mansion. They are usually red or purple with Shy Guy masks, and are equipped with pitchforks resembling those carried by Beezos from Super Mario Bros. 2 and the non-Mario game Yume Kōjō: Doki Doki Panic. When Luigi uses the vacuum on them, the masks come off revealing two yellow eyes and a small black hole for a mouth that are actually set on the hoods that they wear. Removing their masks also allows them to be stunned with the flashlight and vacuumed. A group of dancing Shy Guy Ghosts appear in the Ball Room, and the Floating Whirlindas appear after Luigi catches them.
Other similar enemies are Boo Guys and Polterguys.