Finally, after much recounting and reliving your moments of awesomeness, you arrive at what you're pretty confident is the right answer. Probably. Assuming you didn't miss any secret passageways or a set of stairs to a whole extra basement level.
You spin the dial to the number you've settled on and press the button in the center before you can get any less sure. It sinks into the door at your touch. Something starts to click as hidden gears begin to move and make the decorations across the door spin and contract. Monsters on either side of the center divide pull their claws back from the seam.
The clicking stops, the movement freezes, and...
...the doors swing open wide! The sudden light and noise blaring through strikes you blind and deaf. As your senses slowly adjust, you realize what the noise is.
Applause. Thunderous applause.
You stride into the highest room of the tower and finally see what awaits you. The room is set up like the red carpet walkway at the royal palace, but with a decidedly Nightmare Night style flair. The black and orange carpet is surrounded by more carved pumpkins than you can count, all of them enchanted to whistle and whoop and holler as you pass like you're some kind of Bridlewood celebrity.
Floating alongside the path are a dozen fancy mirrors, each one showing a familiar face. A werewolf mare. A giant rabbit. A fat, balding stallion in a mask. A grizzled pegasus in uniform. And more besides. They all cheer you on and applaud your victory as you strut down the aisle.
The path leads you to a massive hole in the wall. The view from here is fantastic. The whole of the haunted house is spread out below you; you can practically trace the path you took! Beyond it you can see Ponyville, shining like a star just over the next hill. The wind ruffles your mane as you gaze down upon it all.
It's... peaceful.
Now how do you get down?
"So do I just fly back or— oh!"
Before you can finish asking, a sheet of rainbow light appears beneath your hooves. It grows quickly, curving around the tower and out of sight.
Eh, why not? With a whoop you take a running start and hop onto the magical slide. It circles the tower three times, always forming more just ahead of you, then takes two lazy circuits of the whole building before depositing you outside the front door, right back where you started.
"Congratulations, Rainbow Dash!" Starlight applauds as you land. It's double the applause, as she's split back into Red and Blue versions. "You're the first pony to finish a full run of our haunted house!"
"Strictly speaking, our first participant too." Blue Starlight adds. "So, were you scared?""
"What, me? Scared? Pft! It was a piece of cake." You're not about to admit just how many times you came close to breaking. "But to anypony else, that'll scare the wings off of them! It was awesome! You must have worked like crazy to pull this all together."
Red Starlight blushes slightly while Blue Starlight scuffs a hoof on the ground. "I mean, I did my best. It was a group effort. I couldn't have done it without Trixie's help with the illusions."
You push through Blue Starlight (who pops into nothingness) and drape your foreleg around her withers. "Come on Starlight! Take some credit for your hard work! Those were some intense illusions. I thought I was actually going to die a few times."
Starlight merely blinks at the space her double used to occupy. "How did you still know she wasn't real?" She turns to you suddenly, alarm painted across her features. "Wait, you thought you were going to die?"
"She didn't have a shadow," you explain.
"No, no, forget that. Why did you think you might actually die? It shouldn't have been that scary!"
"Well all those spells that make you forget you're doing a haunted house and think it's real kinda amps it up. Especially the ones that put fake memories in your head."
Starlight's face goes as white as a sheet. "That sounds like confundus and memory spells. But I didn't put in any..." Her face flips from white to red as quick as if someone hit a switch. "Oh no she didn't. Excuse me, Dash. I need to go have a little chat with my cohost."
She lights her horn and vanishes in a sparkle of magic. Though she doesn't go very far, as you can very clearly her shout of "Trixiiiiiiie!!!" from inside the house. Though that kinda leaves you in the lurch as to what to do now.
"Hey Rainbow Dash!"
As if summoned, at just that moment your friends arrive over the crest of the hill, all decked out in full Nightmare Night regalia.
Rarity you're pretty sure is a princess, though it's hard to figure out which when the only clue is a big carmine line running through her dress. Pinkie's come as some kind of plant pony with a large flower growing out of her back and vines twined around her legs. AJ is clearly a changeling... but in a snow parka? It feels like there's a pun or something there that's going over your head. Fluttershy, who's really putting her bravest hoof forward this year, has gone with a classic sheet ghost. Probably to make it that much easier to hide at a moment's notice.
And Twilight...
"Uh, hey, Twilight? Did you... turn your back legs into swords?"
She groans at this even as her incredibly pointy-looking hooves prick the ground. "Why does everypony think they're swords? They're scissors. See the screw over my cutie mark? I'm Edith Scissorhooves, from the novel of the same name. But the way ponies have been reacting tonight, you'd think nopony has read the greatest piece of neo-gothic literature to come out in the past twenty years!" She kicks at the ground, accidentally slicing through a few sticks. "It could be my fault though since my costume's not strictly canon-accurate."
"She had to turn her front legs back inta normal hooves," Applejack explains. "Couldn't keep her balance."
"Well book-accurate or not, I think it's a lovely costume."
"Thanks, Rarity." Her feelings reassured, Twilight turns to you. "No costume for you this year?"
"No I got one, I just didn't want to put it on before I tried Starlight's haunted house." Which, as it turned out, was an astounding bit of foresight. You probably wouldn't have been able to pull off half as much fighting if you'd worn your cyborg-pony soldier-from-the-future costume.
"Oh my," says the sheet with holes. "So you've already explored the whole house? Is it-is it really scary?" Her voice keys up to a high squeak as she finishes the question.
You reflect on all your recent escapades. Fighting monsters. Running from insane ponies. Facing almost as many social and mental situations as genuine horror ones. Then you imagine Fluttershy in your place and wince. "Yeah... this is probably gonna be too much for you, Flutters. That's why I went ahead to check it out."
"Thank you. I think I'll wait outside until you all finish then."
"Don't count yourself out yet." As much as you know she needs to be kept away from the worst rooms, you don't want her to miss out entirely. "I know Trixie has a way to turn the fear factor higher or lower. I had it set pretty high, but I'm sure she has a low setting for foals and, y'know, the easily scared. Plus, now I know all the rooms that are safe enough for you. Like the bunny room."
Her eyes light up at the magic words. "There's a bunny room?"
"Now you've done it!" Pinkie giggles. She jumps in place, making her leaves rustle. "Guess we're all going in then! It's an adventuring party! I call being the druid!"
"Are you sure you want to go back in?" Twilight asks. "If you just finished it then it probably won't be nearly as scary the second time."
A slow smile works its way onto your face. Sure, you know what's coming, but who's to say that every exploration will be the same? They might make different choices than you did. Choose to befriend where you attacked, or use items you didn't have yet. And especially important: for the rooms where you do know what's coming, you get to watch their reactions to it!
A stray thought stops your mental train in its tracks. Is... is this what it feels like to be Trixie? Watching someone explore from above and giggling where they fall into the same mistakes you did? Huh. Kinda casts her in a different light.
But you've been stalling long enough. Twilight and the rest are still waiting for an answer.
"Absolutely. Let's go! You guys are gonna have an awesome time. I guarantee it!"