You.
...You must think you're awfully clever.
Don't play dumb. I told you, when you first moved here, you must never contact anypony in the outside world ever again! Now your little sister, that gullible little sycophant-
...Oh, I haven't done anything yet. But she and her friends have begun a very foalish journey. In fact, I just watched them board the last train to the west ten minutes ago...
...Yes, that's right... they're coming here... They think they're going to some magical place to bring you back from the dead... HAH!
...Soon, if they don't turn back, they will be just as damned as you. Unless... you tell me how you breached my security measures...
...Still feigning ignorance, eh, best friend? You know I know you're smarter than that.
But I can wait. I can draw it out of you... I have plenty of methods to make you talk...
~
"Scootaloo, this is ridiculous! And disgusting!"
Applebloom wasn't sure why she was still arguing. The three of them, led by Scootaloo, had been climbing up the bowels of the mountain for the past hour now. The icy, slick concrete had swallowed them in total darkness, bioluminescent green moss being their only source of light until Sweetie Belle formed her magic into a glowing orb on the tip of her horn. They walked on a path of raised metal grating to the right of the wastewater, the sounds of their clanging hooves drowning out the sloshing and churning. But as they ascended they would occasionally stop in their tracks, their ears flicking in response to what sounded like stale, trapped gases and winds blowing through the pipes, producing airy, distant shrieks and howls.
"Ugh, I'll never get this smell out of my mane," Sweetie whined. "Do we really have to go this way?"
"Water follows gravity and flows downwards," Scootaloo spoke as she walked stoically forward. "And upwards is where I'm going."
"Ah know you wanna git to that "place where the dead are given new life", Scoots, but lookit us!" Applebloom tried to reason once more. "We're in a buckin' sewer fer Celestia's sake! Surely there's an actual cave we coulda gone in instead, or maybe even a different path on th' outside!"
"Although... that crazy mountain stallion out there did threaten to kill us," Sweetie frowned. "Besides, we've been in here for so long... do you know how to get out of here?" Applebloom and Scootaloo stopped in their tracks.
"Wait, you weren't payin' attention?!" Applebloom gasped, looking at the others. Sweetie shook her head.
"Um... I've just been focusing on going up..." Scootaloo admitted sheepishly.
"Well, ain't that just great. The Cutie Mark Crusaders... lost in a stinky sewer," Applebloom pouted.
"We'll be fine..." Scootaloo waved her hoof as she turned back to the path ahead of her. "All we gotta do to get out is just go downwards."
"What are you gonna do when you even get there-" Sweetie's question was cut off by another phantom scream floating through the sewer's pipes. They gulped collectively and let a few moments pass before walking again. "...Do you really think Rainbow'll come back from the dead?"
"Sweetie..." Applebloom groaned. Scootaloo stopped again, prompting her friends to do the same.
"...You know... I'm really not sure what will happen," she finally said, her voice shaking. "She's gone... I know. I watched her... and I miss her so much. But this book, it... it just knows so much about us. All the hidden messages, all the memories... and this place she and Twilight went to, the things they never told us about, never wanted to tell us about..."
She is still alive.
"I... I just can't... I can't ignore it. Something keeps telling me she's there! She's really there! I just need to go there and find her! I need to go there and bring her back! S-Somehow..."
She touched the urn through her saddlebags. Nothing happened, but Applebloom and Sweetie Belle did move forward and lay a hoof on her back. They gazed and nodded sympathetically at Scootaloo, silently reassuring her. She quietly sobbed for a few minutes to regain her composure; once she was ready, they set off again.
~
Another hour passed. Any evidence of maintenance work this deep in the sewers became entirely nonexistent. The luminous green moss grew thickly all over the walls, emitting so much sickly green light they could have mistaken the place for an evil Changeling hive. They saw what appeared to be a crossroads in the tunnels approaching, providing enough space to rest and comfortably stretch out for a while. Scootaloo quickened her pace slightly, relieved at the sight.
But something knocked her off balance and made her trip. As she stumbled, she heard a rattling noise at her hooves. Looking down, she found a coil of wire stuck to her foreleg, adorned with a few strands of small bones strung like wind chimes. As her friends stopped to help, Scootaloo suddenly heard a fourth set of hoofsteps in the distance.
"Uh... what was that?" Applebloom and Sweetie Belle's ears flicked as they heard the noise too.
"Another pony?" Applebloom suggested. "But what in tarnation is anypony else doin' here...?"
"You should not be here..."
Something menacing echoed. The hoofsteps stopped.
"Um... w-what?" Sweetie breathed.
"You...
...should not be here!"
A swoosh and a roaring voice boomed from behind them. Forgetting all about the strand of bones, Scootaloo and her friends screamed as they ran for the crossroads. Once they reached it, however, they found themselves in a long, damp hallway lined with multiple tunnels along the walls. Some were stacked two, even three high, and pipes embedded in the ceiling were covered in thick grates, each and every one leaking out a trickle of wastewater through a tangled stalactite of glowing moss. Their eyes darted around frantically, trying to pick out the best place to hide.
Another swoosh, this time louder. Scootaloo ran into the fourth pipe on the left. Looking behind her, she gasped as she saw Applebloom run further down the hallway while Sweetie ran into the seventh pipe on the right. She stopped and called out to them, but a fleeting black shape shot past the tunnel's opening, forcing her words back down her throat as she turned and ran again.
About thirty feet in, she found herself in a narrower hallway. Her heart sank as she looked around; the other tunnels on the left side of the crossroads emptied out into this same hallway, while one other tunnel in front of her led ever deeper into the sewers. This was quickly confirmed by a screaming Applebloom shooting out from the furthest tunnel down the hallway and running towards her, her eyes widening as she saw her and realized the same thing. Maybe it was different on the right side?
A growl of frustration belonging to none of the three Crusaders echoed throughout the tunnels. Scootaloo joined Applebloom as she ran past, and they ducked down another tunnel in order to reach the other side, hopefully finding Sweetie in the process. But they ran past the crossroads and down an opposite tunnel, and found a similar layout on the other side.
"Aw, come on! Whut is this?!" Applebloom shouted. Sweetie's screams echoed throughout the tunnels, turning Scootaloo's blood to ice. She and Applebloom made haste down the right hallway, but as one ducked into a different tunnel than the other, they were separated once more. Scootaloo hoped to see her again as she ran towards where she thought the scream had originated from, but Applebloom did not exit her tunnel into the crossroads. Hopefully she had only turned back to check an adjacent tunnel.
She made it to the left hallway, only for Sweetie Belle to collide into her barrel and knock the both of them over. Once they had scrambled back to their hooves, Scootaloo breathed a small sigh of relief, only for her breath to hitch in her throat as they heard a vicious snarl and Applebloom yelling in the distance.
"Get over here...!"
Sweetie's horn lit with spring-green magic in preparation as they ran back down the tunnel. They stopped once back in the crossroads, taking a moment to determine where Applebloom might be. But suddenly a rushing, rumbling noise sloshed high above, making bits of dead moss overhead rain down upon them.
"Sweetie, what'd you do?!" Scootaloo glanced around.
"That wasn't me!" she quivered. Somewhere, Applebloom yelled again. Even more chillingly, a tortured, raspy voice echoed from a pipe directly above them.
"You... You do not belo- ...wait a minute..."
Before Scootaloo could process the words, a deluge of water began pouring from the grated pipes above. Sweetie's magic quickly formed into an umbrella as they ran into the nearest tunnel to the right hallway, but the water quickly began to flood the maze of pipes. Bits of glowing moss and rotting garbage swished past, the water collecting and running along the ceiling and dripping down onto their heads. They were nearly floating by the time they reached the hallway, and they quickly pulled themselves into the dampening tunnel above. In only a few moments the water began to rise once more, forcing the two back into the hallway as to not get trapped. Together they struggled to stay close and afloat, screaming in terror, violently slapping, kicking and treading water as it rose to the third tier of pipes and began to rise even past their floors. Between gasps and coughs for air, Sweetie's magic eventually morphed into an air bubble around herself and Scootaloo, and they watched in floating horror as the water rose all the way to the top of the ceiling with no sign of drainage. The luminous moss glowed intensely from the flood, nearly blinding the two.
Scootaloo shivered in the damp air. "How... How long can you keep this up for?"
"I don't know..." Sweetie breathed heavily, straining to keep the water out. "It's really hard... maybe five minutes at the most? ...Wh-Where's Applebloom?" A wave of dread washed over Scootaloo.
"S-She's not... we d-didn't... oh Celestia, no..." The image of Applebloom scratching at the pipe grates on the ceiling as the water rose above them stamped out all her other thoughts. Even if she could hold her breath, how long until the water drained enough? Tears began to moisten her eyes, and Scootaloo's breathing grew shallow as another image etched itself into her mind: an image of one of her best friends floating back down with the draining water as a lifeless, bloated corpse.
And it was all her fault.
But she didn't get much of a chance to mourn. Suddenly a coughing, gagging Applebloom appeared, roughly shoved inside the air bubble by an unknown hoof. Then, just as quickly as it had happened, the bubble began to move swiftly through the water. As Sweetie struggled to maintain her spell's integrity, Scootaloo blinked away her tears.
Just outside the green-tinted magic swam a Pegasus mare, but not one she recognized. Her coat was a filthy shade of cool grey, and her mane and tail were matted, dripping, tangled ropes of dark magenta and darker pink, with similarly-dark purple eyes and a Cutie Mark of a baby bottle. She wore endlessly patched and tattered saddlebags around her barrel, and a clear plastic bag over her head with string tied around her neck to keep it in place, presumably to obtain a couple extra breaths while she shoved at the air bubble with her front hooves and flapped her wings to swim faster.
Applebloom soon found herself silently staring at their savior as well, but Sweetie groaned and clamped her eyes shut as she funneled as much magic into her spell as she could. Around them, her air bubble's walls rippled and wavered; she was quickly tiring herself out. Scootaloo hoped she could hold it for long enough as the Pegasus mare directed them down towards a dark tunnel, and they swayed blindly in the currents like an eel.
Only a minute later, Sweetie began to cry out in exhaustion as the bubble began traveling upwards. No sooner did Scootaloo feel herself being launched out of the water that the spell finally broke, and the air bubble burst. A sudden brightness forced her eyes shut, but she soon reopened them as she realized she was on solid ground.
She found herself in the back corner of an oubliette the size of a barn, aglow with moss and a small, dying fire kept within an old industrial-sized metal mixing bowl. In one corner was a broken desk covered in papers with a half-burnt candle beside them; in another corner were cracked crates and barrels filled with various supplies. In yet another corner was a large pile of rags, roughly arranged into the shape of a bed.
But none of this really mattered at the moment. She rushed over to Applebloom and Sweetie Belle, scooping them both into a tight, tearful hug, which they returned. A cough interrupted them shortly, and they looked over towards the mysterious Pegasus mare as she untied the bag from her head, shook it out and placed it back inside her saddlebags before taking them off and setting them aside.
"You..." she finally spoke. Her voice was caustic, raspy and gravelly, as if she had a serious sore throat. "How did you get down here? Are you escapees? You don't appear old enough to be one of them..."
"Who... who are y-you?" Scootaloo stuttered, realizing that she and her friends were now at this pony's mercy. The mare took a moment to turn away and cough.
"...Accoucheuse," she finally answered. "Ugh... to be caught during the evening shift's preparation, you're lucky I was tracking you three."
Scootaloo and the others shared worried glances at each other, not knowing how to respond.
"Well... none of us are going anywhere for a while. Might as well rest up for later... go on," Accoucheuse waved her hoof, "I am not your enemy here."
Not wanting to offend the mysterious sewer mare, Scootaloo nodded, and she and her friends sat down by the fire. She began to open her dripping saddlebags for some rations when a flash of realization made her heart leap to life. She gasped as she frantically dug through her belongings, found the black-lacquer box and opened it secretly, carefully unraveling the slightly-damp towel.
She is still alive.
The urn was dry, undamaged. Breathing a deep sigh of relief, Scootaloo repacked the precious item and replaced it in its hiding spot, safe from the world.