From the Super Mario Wiki
The Strong Poltergeist (Strong Boffin in British English versions) is a sub-boss that Luigi encounters in Luigi's Mansion: Dark Moon. It is an orange Poltergeist covered in the stony texture shared by other "Strong" variants of ghosts. The mansion it is fought in is Treacherous Mansion. When Luigi gets to the Study, he finds a book key that will unlock a door that leads to the Train Exhibit where Mario is supposedly held. Once Luigi puts the key in the bookshelf, the Strong Poltergeist comes out of the shelf and takes the book to the Space Exhibit. This sub-boss has 200HP.
The Strong Poltergeist is similar to the normal Poltergeist, but strengthened by crystals from the Secret Mine. It is very similar to the original Poltergeist but has the ability to head into space and transport Luigi there as well.
For Luigi to battle it he looks through a telescope which warps him into space where he battles the Strong Poltergeist. The Strong Poltergeist travels around the room throwing stars. Luigi must dodge these and shine his Strobulb on the Strong Poltergeist. After escaping the Poltergust 5000's suction, it goes inside the asteroid in the center and throws bombs at Luigi. Afterwards, it will get out and start throwing stars again.
Ghost Container Description
"As if they weren't enough trouble already, the crystals have augmented these brainy ghosts' telekinetic powers. I wouldn't want to run into this guy in a dark alley. That's for sure."
Names in other languages