Professor E. Gadd tells Luigi that after capturing Big Boo, the Parascope began to pick up radical new signals, a distortion in the fabric of their dimension -- a paranormal portal that appears on the Terrace in the Treacherous Mansion. The professor believes that the last Dark Moon piece is beyond the portal, stating that is why they haven't found it. He also adds that Mario and King Boo may be there as well, but warns Luigi that entering a paranormal portal is "extremely dangerous, but they don't have a choice". Luigi is then teleported to the first floor of the Inner Courtyard in the mansion.
In the Inner Courtyard, Luigi makes his way up the spiral staircase to the upper floor and goes through the door to the Terrace. At the Terrace, he sees King Boo using his jeweled crown to fire a bolt at the space above a golden altar, opening a large portal which he then goes through. Soon after, many Strong ghosts begin flying out of the portal. E. Gadd then contacts Luigi in shock, saying that the paranormal levels have now "shot through the roof" and telling him that the portal will have to wait for now until the ghosts are captured, or else their dimension "could collapse upon itself". Throughout the rest of the mission, pink flashes of lightning will constantly occur.
During the mission, E. Gadd will provide the locations of the paranormal activities to Luigi on the Dual Scream's map. The rooms infested with ghosts will start off green and as time passes will change to yellow then red if the rooms are not yet cleared. Luigi can also see meters of paranormal levels for each individual room on the objective screen, ranging from yellow for the lowest to red for the highest. If the paranormal levels in the rooms reaches a certain limit, or if a single room's paranormal meter is completely filled, Luigi will have 3 minutes to capture the ghosts for the levels to stabilize, or else it will result in a Game Over. Luigi can also make ghost capturing quicker and easier should he use the E-Gates in the mansion's Front Entrance to navigate from room to room.
Luigi first heads to the Nautical Exhibit and Space Exhibit. After clearing the ghosts from the two rooms, E. Gadd contacts Luigi of ghostly activity on the first floor, in the Jungle Exhibit and Ice Age Exhibit, specifically. After Luigi clears one of the exhibits, E. Gadd will contact him again of more ghostly activity, this time in the Ancient Exhibit and Dark Age Exhibit as well. When Luigi steps foot in either of those two exhibits, E. Gadd will contact him again revealing that the Restrooms and Kitchen are also infested.
When all of the infested rooms are cleared, E. Gadd will tell Luigi to go back to the Terrace as he is picking up "mighty strange readings" from there. When Luigi makes his way up the spiral staircase in the Inner Courtyard and back to the Terrace, a horde of ghosts will come out of the paranormal portal, coming after him in constant waves. After capturing all of the ghosts on the Terrace, E. Gadd commends Luigi, calling him a "ghost-catching artist" and telling him to come back to the Bunker to unload all the powerful ghosts before stepping into the portal.
E. Gadd figures that King Boo "flipped out" when Luigi defeated Big Boo, and sent a horde of ghosts as a last-ditch effort to stop Luigi, but by doing so also revealed his exact location to E. Gadd where Luigi can get to him. The professor tells Luigi that the portal is still open and must hurry before it is too late.
King Boo has sent a horde of ghosts to start a paranormal riot. Capture all of the ghosts before they become too powerful to be stopped!
In the Aviation Exhibit, Luigi must use the Dark-Light Device on the area where the hot air balloon used to be and vacuum up the Spirit Balls, forcing out the mission's Boo, MaraBoo. This is easier to do before the ghosts are released.
I'm getting strange paranormal readings on the Terrace. We’d better send you in to inspect the place.
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