One unfortunate walk back to the Mansion later...
Luigi was creeping up the steps into the nuthouse when suddenly Mansion called out. "Hey, mortal! Your mother just called. She says you should give up unconditionally. And also you're not wearing the right size of overalls."
Luigi frowned and glared up at the house's glowing eyes.
"I have enough mocking objects in my life that are supposed to be inanimate, okay?? So you can just go back to... um... being a house," Luigi said, trying to be stern but failing miserably. "And what's in this for you, anyway? Why do you want me ded??"
Mansion conveniently didn't reply, so he ended up looking like a dork who talked to houses.

Mansion: The inner machinations of my mind are an enigma.

Mappy: Ironic. I could say that about a few other people here too.

Luigi: What are you implying??

TC #2: Hey, but that's a good point. What are Mansion's motives? Who's the real enemy here?

Author: Stop jumping ahead of the plot!!

Anyway
When Luigi got back inside Toad was still playing Pokémon, which makes sense because he was doing that three minutes ago when Luigi previously passed through.
When he got there the Game Boy Horror immediately started beeping. But it wasn't the awful annoying ringtone, it was softer and more insanity-inducingly repetitive this time.
Blip-blip-blip-blip-
Sorry. I need to work on not doing that.
"Hey, what's that sound coming from my pocket?" Luigi asked, spinning around.
(You see, kids, this is before cellphones were invented.)
"Isn't it that boo radar?" Mappy asked.
"Oh. Maybe." Luigi pulled out the GBH and held it up, watching the tiny light on top flash red like a siren.
blip-blip-blip-blip-
"You think that's important?"
"Well, I don't know—DID YOU HEAR A WORD THE PROFESSOR JUST SAID??!" Mappy scolded.
"Ohhhh!" Luigi said. "So it works like a metal detector! I've seen these before!" Holding it up, he began rubbing the game boy all over the walls like a paintbrush.
You know, like we did all the time when we were kids.
"Hey Luigi, are you going to take care of those boos now? Because I want my fifty bucks back," Toad spoke up.
Luigi did a double take and paused. "What fifty bucks??"
Toad blinked at him and smiled sweetly. "The fifty bucks that is definitely still in my pocket," he replied pleasantly. "So why don't you go clean up house, Luigi?"
Luigi frowned. "Oh, is that some kind of clever pun? Because I'm like a janitor with a vacuum now? Is that what I've been reduced to in your eyes, Toad??"
"It's an improvement on toilet scrubber," Mappy muttered sidewise.
"You're not helping!" Luigi scolded. "...And you know what? No! I'm not gonna go catch those boos right now, because I say so! We're gonna go bust down some doors and take some names! ...Whatever that means!" He grabbed the Poltergust and cocked it like a rifle.

ONE VERY BOSS WALKING MONTAGE THROUGH THE HALLWAY LATER...

The door to Clair's room busted open on the hinge like eggs on Easter morning.
"Ghost police!! Nobody move!" Luigi hollered, slinking inside like a weird cartoon character. Holding up his vacuum, he aimed the hose at the chair where his former dance partner was sitting, still trying to make sense of the story script.

Author: Much like I myself :)

Luigi: Why does this make me feel... so much worse?

"You there! Where might I find some lead concerning my less-tall, less-trim brother?"
Clair looked up at him in boredom. "Oh, it's you. Come back to Rickroll me again?"
Luigi shrugged. "No, that was Mansion's doing."
"I don't really care about the particulars," she replied. "So, I've got the pages all mixed up, and I can't really tell you where to find your brother, but if he's not already an entree in King Boo's three-course meal I'd say you can proceed by heading in this door to my left." She pointed.
"Oh, the professor already said they wouldn't eat him," Luigi informed. "So I guess we'll take the door. Thanks, sweetums," he waved, heading along.
She rolled her eyes. "Luigi, the dance segment is over. We're not interested in flattery anymore."
Luigi frowned and moved ahead. "So are you going to kill me now, or do we just split ways like normal people?"
Clair considered. "Neither. You're going to keep coming back to me for advice when you find random pieces of clothing around the house."
"Oddly specific, but okay," Luigi agreed. Then he proceeded to the next room.

The Next Room

The next room was called the mirror room, and I bet you can never guess the reason for that.
Go on, guess. I'll give you a hot second.
...
...

...OKAY IT HAD A GIANT MIRROR ON ONE WALL THAT WAS BIG ENOUGH TO REFLECT THE DEATH STAR'S LASER! OKAY?!
...Luigi stepped in and the first thing he was greeted with was the blip of the boo radar and the charmingly terrifying sound of his own voice.
Or rather, LR's voice.
"Heyyy, it's my host man Luigi! How's it going?" his reflection asked.
"I'd rather you don't talk to me," Luigi replied as he strode into the room. It was literally an empty room with a mirror, minus a couple of pieces of useless furniture that included a giant fire pit or torch holder on a stand.
"What, are you still upset about that boo incident?" LR asked. "Luigi, you've got to learn to let bygones be bygones. You had to open that hatch, you know."
"And I also just had to receive that dumb letter in the mail this morning?" Luigi questioned grouchily.
"Hey!" Mappy snapped, offended.
"Quiet, you!" Luigi retaliated. "You know, I've been thinking about this, and there's no reason for me to trust you, too, Mappy! You came straight from King Boo!"
Mappy was still. "How DARE you accuse me! I thought you didn't believe the boos were behind this trap!"
"Well, maybe I don't know anything anymore!!" Luigi snapped back. "And will someone shut this thing up??" he throttled the GBH which was still going off.
Blip-blip-blip-blip-
LR cleared his throat. "Luigi, I understand you have issues, but shouldn't you be catching those boos right now like E.Gadd said?"
"No! Because I already decided I don't feel like it, and no one can make me," Luigi said stubbornly. "Now what's the purpose of this room, to annoy people to death with their own reflected likeness??"
LR crossed his arms. "What, you've never heard of a mirror room before?"
"Can't say I have, not really!" Luigi replied.
"Well, how exciting! Let me be your guide..." LR stepped back and Luigi was afraid he was going to start another musical number when—
Oh no! Like a wonderful dream that could only happen in a Japanese businessman's imagination, a creepy-cute ghost appeared in the mirror behind him, causing Luigi to scream and pull out his weaponized vacuum cleaner in terror!
Because that's what drives up sales, folks!
Turning the Poltergust on the ghost, Luigi was surprised to find that it did nothing. Instead, it merely hovered there, sadistic smile leering over LR's shoulder.
"Hey, uh, Luigi," LR said. "Don't mean to bother you, but do you have any idea how mirrors work?"
"Yeah, why?"
"Because I need you to use your brain again."
"Aw man. I hate doing that."
"No kidding," Mappy input.
Luigi took a page from E.Gadd and ignored him. "So the ghosts appear in the mirror and NOT in real life? Well THAT makes a lot of sense!" he yapped. "That makes everything reverse for me!"
"I'm sure you'll just die," Mappy told him.
Smack. And then Luigi got punched from behind by the ghost, his health meter was reduced all the way to zero, and he hit the floor and died.
Thus did Super Mario, and the entirety of the great Mushroom Kingdom, fall.

Toad: Well that was inspirational.

Game Over

....

What? We told you it was game over. That's gamer talk which means the story's over and you can get back to your busy lives with much more important things to do, like making lunch. Or doing laundry. Or homework or paying bills or watching football or picking your nose.
Or basically ANYTHING other than reading a crackfic about an Italian boi's fictional struggle for sanity in a stoopid Mansion.

Luigi: FICTIONAL?? I'll show you FICTIONAL, pal!!

Mario: Yeah! This isn't playtime at the rodeo!! THIS IS LIFE OR DEATH!!

King Boo: Technically, Luigi's dead now, so he shouldn't be allowed to talk.

Luigi: Am not!

King Boo: Do you wanna be?

Luigi:.......

Whew.
It's good to have a reality check every once in a while. How are y'all doing? Great? Good. Now let's-a-go.

JK LUIGIS NOT DEAD!! Scrambling up as if hit by a basketball, Luigi gasped for air. "What.. just... happened?? I feel like my soul departed for the netherworld but was punched back into my esophagus before it could get there! That was weird!"
"Not the weirdest thing I've heard today," Mappy said, unimpressed. "Now if you'd pay attention we've got company!!"
Spinning around, Luigi tried to see the invisible ghosts in the mirror reflection. Spotting a tiny round spirit that looked like its tail was on fire, he aimed for that.
"Hey there's one! Hah! It looks like an orange!"
POP. He sucked it up and a big red coin of some sort fell out onto the ground in front of him.
"Hey, what's this? Looks like the Poltergust is falling apart," Luigi commented, bending to pick it up. "Figures, since that Gadd built it."
"HEY! That's no way to talk!" An unfamiliar voice, odd and echoey, suddenly emitted from the end of the vacuum nozzle. Screaming like a chipmunk, Luigi dropped it and tried to back away, except it was strapped to his back, so he looked like one of those dignified cats who is terrified of the plastic bag caught around his foot.
"Wh-who said that??" he asked.
"I did. Poltergust!"

Mappy: Why am I not surprised.

Author: What? I let you talk!

Luigi gasped and picked up the nozzle. "Poltergust?? You can talk??"
"Of course I can. Now don't worry, Luigi, I'm here to help."
Luigi frowned. "Well, yeah, you have been for a while now technically," he said. "Why didn't you say something before??"
"I can only talk sometimes," Poltergust replied. (Because that makes sense.) "Now listen. That's a fire elemental medal. Whoever carries that will be able to see and use the elemental fire ghosts and burn things as they please!"
"Whoa, time out," Luigi said. "Burn things? Well what are we waiting for, let's start a fire and burn all these doors down so I can find Mario without risking my hide!"
Mappy paused. "Wouldn't starting a fire in here already be risking your hide?"

Mansion: Careful, knave. Next person to commit arson on my property doesn't even get a funeral.

Poltergust coughed. "Uh, yeah, that's not really... allowed," he said. "But it'll come in handy, definitely! Why don't we try it out?"
"Way ahead of ya, Buddy," Luigi said, brandishing the nozzle of his new friend.
Poltergust exhaled a column of flames. "FIRE ME UP!!"

Mappy: Oh sure, give him a talking WEAPON and it's all Buddy-Buddy.

Luigi: Jealous much?

Mappy: Well I don't think it's a secret that you treat me like dirt!

Luigi: So, you're jealous.

Poltergust: I realize that this is awkward...

Mansion: This is what happens when you talk to everything.

Luigi: Says the giant sentient house.

E. Gadd: Luis!! Quit talking to your inanimate objects and get to work!!

Luigi: Yes sir right away!!

Then, screaming like a lovesick banshee, he opened fire on the ghosts in the room and sent them all to the post aftergame with his flames of justice.
Unfortunately just then the GBH rang like we all love so much.
MEEMAWMEEMAWMEEMAWMEE—
"Have mercy!" Luigi yapped, picking it up and glaring into the screen. "Yeeeeeello!"
E.Gadd was wearing a not-lovely expression. "Luis, I told you not to answer the phone like that again."
"And I decided to disregard you," Luigi replied.
E.Gadd ignored him. "Anyway, what's that you've found there?"
"Fire elemental medal," Luigi said in boredom.
"Oh... looks like it's a... fire elemental medal! Wonder what it does...?"
"Lets me see the fire ghosts so I can catch them and spray fire like my pyromaniac brother," Luigi said.

Mario: I heard that, and it's not over.

E.Gadd ignored him. "According to my research, it grants its wearer the ability to see fire elemental ghosts! They show up wherever you see fire, my boy. They're ghosts of fire itself, if you will. They tend to get surprised by your presence and leap out into the air. That's your chance to suck em up... you may have to use that fire to catch certain kinds of ghosts too... don't say I never warned you!"
"Believe me, I'm warned," Luigi groaned. "And by the way, how come you never told me that Poltergust talks?"
E.Gadd stared at him like he'd stolen his milk money. "Loogy, why would you even presume that the Poltergust talks."
"Because it does?"
E.Gadd sighed and pinched his nosebridge. "Look kid, artificial intelligence is still one year away. And although I already knew you were crazy, now I know you are."
Luigi frowned in confusion.
"So just run along and play with your imaginary talking friends, okay?" the professor said. "I've got to take my cake out of the oven before it burns. Later!" And he punched the button.
Luigi gasped, offended. "Cake?! I wanted cake!!"

Mario: I'm going to say, from experience, that cake is only for the strong at the end of their life-changing adventure.

Author: SHUT YOUR—

Ahem. Wearing an irritated expression as was befitting the moment, Luigi hung up the Poltergust nozzle and watched as the lights came on. LR stood up from where he'd been hiding in a corner of the mirror.
"Thanks, bro! You saved me!"
"I'm not your bro," Luigi said grouchily. "And right now, if you were my bro, I'd slap you in the face for getting lost."
And then the boo radar went off again.
Blip-blip-blip-blip-
"AAAUGHHH!!" Luigi gasped like a choking piranha plant, grabbed the Poltergust, and blasted the GBH with a wave of fire.
(Not really.)

E.Gadd: Yeah, that would be a really dumb move. Given that it's the only way to track boos and contact me and all.

Luigi: What an utter loss that would be.

Anyway, Luigi went back into Clair's room, GBH still beeping from his pocket. Rubbing his eyeballs, he moaned, "I'm beginning to see why the professor was so happy to give this to me."
"Yes, he also has a Ph.D in subtle torture," Clair spoke up.
Luigi groaned again.
"Now cheer up, Luigi. I have something for you," Clair said now.
"Really? Five pounds of biscotti??" he asked excitedly.
"Better! A key to the laundry room!"
Luigi deflated like a sack of rotten potatoes. "Joy."
"Just take it," she sighed, shoving it in his hands. "You'll probably need it where you're going."
"Um, thanks, but I already went to Diaper Land, and it's not gonna make a great Mario Kart track," Luigi told her.
Blip-blip-blip-blip-
"And do you have any idea why this thing won't be quiet??" he asked.
Clair frowned, taking the GBH from him. "It's a boo radar, correct? So it beeps whenever something round like a boo is nearby. That's how it works."
"Wait, like a boo?" Luigi interrupted. "Not just boos?"
"It would seem to be," Clair replied.
Blip-blip-blip-blip-
In terror, Luigi held the game boy over her magic bowling ball. The blipping got progressively more loud and angry.
Then Luigi grabbed his own eyelids and yanked them over his face in horror.
"OH IM IN PURGATORY!!"

Moments later~

When Luigi stepped into the hallway again with key and elemental medal in tow, he was relieved to find the boo radar stopped.
"This is just great. This is just dumb," he muttered to himself. "How am I supposed to find the actual boos in this place if the radar leads me to every single round object in a mile radius??"
Angrily storming down the hallway, he said, "Poltergust, are you alive?"
No answer.
"Hah! Who's the faithful companion now?" Mappy snickered.
"Oh yeah?" Luigi asked. "Well you can't do this!" Then, pulling out his weapon, he blasted a column of fire into the air, which accidentally hit the wallpaper and caused a shred of it to crinkle to the floor.
Mansion shrieked in disbelief.
"AAAAHHHH! YOU MANIAC! YOU BURNED IT UP!!"
"No, admittedly I cannot," Mappy said.
Grinning with a sneaky idea, Luigi proceeded down the hallway with torch upraised, blasting fire every few seconds. "That's right! Don't mess with me or you get fired!"
Mansion was not listening to sabotage. "Naïve green bean, hear my words," he boomed. "If you so much as burn down one beam of my interior I will personally send an army of undead mutants to ransack your house. ...Your actual house."
Luigi slowly lowered the Poltergust.
"Good, that's what I thought," Mansion chuckled.
"But... this isn't even fair! The Poltergust is all fired up and I can't even do anything with it??"
Grabbing the nozzle and shaking it in front of his face, Luigi glared. "You're fired!"
"Yess!" Mappy cheered.
Luigi rolled his eyes. "That's not what I—
"Shh!" Mappy interrupted. "Did you hear that??"
Luigi stopped. "What?"
For an odd, unusual second, no one made noise.
Then they heard it:
"OOOooaaAAAHHHhhoooooghhhhaaHAA!!"
Luigi nodded slowly. "Yeah. I haven't eaten in a while."
"That's not your stomach!" Mappy hissed. "Look! Up ahead!"
They looked. Sure enough, a shadow stretched across the wall like a vampire at a windmill convention... or something.