Hit Rock Bottom
Like other Toads before, the Toad Luigi saved in the previous mission brought back a security-camera image. After Professor E. Gadd processes it, it shows several Boos trapping a Sneaker, a Slammer, and a Greenie inside of red crystals. He then mentions the odd laughter Luigi was talking about, and wonders if it came from the Boos' leader, but realizes that the only way to be sure is to examine the Crystal Quarry.
Luigi gets pixelated once again to the mine, and is sent back to the Airway in order to get to the bottom of the mine. Before he gets there, though, he notices a set of gates that teleport him from place to place which were invented by E. Gadd (whom he also jokes about greeting his other hand). With the help of these gates, he arrives at a room that is nothing but a long slide down; once he gets to the bottom, Luigi realizes he's nearly at the bottom of the mine. He goes into the Smuggler's Hideout, a nearby room, and is attacked by a team of Greenies and a Sneaker. After this, he arrives at the Shaft, which is a long elevator down, and he sees a Greenie, two Slammers, and a Gold Greenie (only the Gold Greenie is able to be captured) holding large red crystals.
Once he arrives at the Deep Hall, E. Gadd calls Luigi and tells him that he's at the very bottom of the mine, and that the Crystal Quarry is somewhere nearby. After obtaining burning rocks and wood, Luigi melts some ice which was blocking a key, obtains it, and unlocks the door to the Crystal Quarry. Upon entering, he sees that the Boos and the ghosts trapped in crystals from the picture are still there, and the ghosts now have white stripes all over their bodies. The Boos flee, leaving Luigi at the mercy of the now strengthened ghosts, but not before taunting and scaring the plumber. Once he inspects one of the crystals, the respective ghost inside it flies out, attempts to attack Luigi, and once it is sucked up, the two remaining ghosts fly out as well. Once Luigi defeats all three, he is called back by E. Gadd, and the mission ends.
This Boo is located in the Chalet. If Luigi shines his Dark-Light Device where the rocking chair by the fire was, Spirit Balls will fly out, and once they are sucked up by Luigi, the Boo, named Booger (Boouncer in PAL versions) flies out.
According to the Toad assistant, ghosts - Boos especially - have been very active in the mine. Perhaps that security camera photo will tell us what they're up to.
Names in other languages