From the Super Mario Wiki
Blue Twirlers are slow, normal ghosts that Luigi encountered in the game Luigi's Mansion. They are one of the largest and most powerful non-portrait ghosts found in the mansion. Blue Twirlers have over-sized fists that they use to make ground pounds, or earthquakes, that spread three feet and take ten HP if they hit Luigi. They have thirty HP each, which can be whittled down by suction or elements.
A Blue Twirler occasionally appears in the Luigi's Mansion Court in the game Mario Power Tennis. They are also found in the Luigi's Mansion stadium in Mario Super Sluggers, where they stun fielders that run into the graves that the Blue Twirlers reside within. Additionally, this ghost appears as a trophy in Super Smash Bros. Brawl.