Their is only one rail line leading to the Crystal Empire, one that had sat unused since its construction a few hundred years ago. For a time after the Crystal Empire's disappearance, the land it had occupied was considered cursed, and no pony dared to trot upon the empty snow. As is common in Equestria however, this was soon forgotten, and sometime after the invention of the train, the vast mineral wealth of the Empire's lands were re-discovered, and overnight hundreds of ponies rushed to the ice, hungry for mineral wealth.
The rail line intended to foster these ponies and their spoils back and forth from this land was but a week completed when Celestia herself declared the land forbidden, not intending the Crystal Ponies to return to a land devoid of livelihood. The ponies, as they always have, requested no explanation from Celestia, and vacated the land without question. The rail line has sat empty since, kept above the snow only by the enchantments placed along the tracks, the kind meant to last.
Such was no longer the case, though, as with the return of the Empire and the upcoming Games, the platform was abuzz with activity. Ponies pushing packages and parcels of products for the upcoming events disgorged from the trains in droves. Few however, boarded the departing trains to leave the land of the ice and snow. Gleaming Polish was one of the few who was, and as such, found herself to be the sole occupier of her chosen train car.
For awhile anyway.
About half an hour into its trip, the train briefly passed through a tunnel, and all the passengers experienced a minute of darkness. When the train left the tunnel and light returned, Gleaming Polish had another pony in the car with her. The pony was seated directly behind her, outside of her sight, but the chill that went down her spine betrayed the mystery pony's presence.
The new pony clearly endeavored to keep out of site, as its garb screamed "I am a suspicious pony up to no good." Its body was covered for nuzzle to hoof in a brown cloak, thick enough to obscure the gender of the wearer. The small amount of hoof that extended beyond the legs were clad in similarly colored boots, padded with the fine shaved fluff of the Crystal Empire's native ewes for soft hooffalls. Even in the off chance one gained a peek beneath the hood, they would have no clue of this pony's identity, for the mystery mare(?) wore a metal mask, with two reflective lenses of light blue crystal.
"Did Striker require much persuasion?" The newcomer asked in a voice clearly distorted by some manner of enchantment cast upon their mask.
"No." Polish responded, unnerved by their sudden appearance but not terrified. "I was the only one of the group without regular employment, so the group unanimously designated me their messenger." Her mood switched to mildly annoyed as she removed a pair of sealed envelopes from her saddlebags. "I've got Coal's instructions safe and sound. I don't need you boys checking up on me."
"New information has come to light, and Coal has fresh instructions." The mystery pony replied, not an ounce of emotion penetrating their cold aura of professionalism. "Twilight Sparkle must arrive in the Crystal Empire with none of her friends, save one. Spike, her dragon assistant, must make this journey with her. She will likely attempt to leave him behind to oversee her library. Persuade her otherwise."
"That would be the dragon everypony saw on Princess Cadance's back after Sombra was destroyed, I assume? Unless the new princess has accumulated a harem of dragon boys and I wasn't informed of." Gleaming Polish chuckled at her own joke, but her mirth was dampened by the cold aura radiated by her visitor, and she quickly piped down. In a more reserved tone, she asked, "So, why is he so important?"
"He is critical to Coal's plan. That is all you need to know."
A few seconds later, the train entered another tunnel, and when light returned to the train car, Gleaming Polish was alone again. She took a moment to review her new instructions, then settled down for the rest of the trip.
It was yet another slow day in the Ponyville library, so Twilight decided she and Spike should spend the time re-shelving the entire collection literature. Twilight's telekinetic tallying of some tomes was interrupted by a hammering knock on the door, causing the books to come tumbling down on the hapless assistant.
Who should greet Equestria's newest princess but an odd pony in a brown cloak?
"May I enter your abode, princess?" The mare asked in a hushed tone.
Twilight was not sure what to make of the situation. "Why, certainly. Also, you can just call me Twilight."
The mare trotted indoors. "I apologize for my odd clothing prin... Twilight. I did not wish to attract attention." The pony discarded her cloak, revealing the sparkling form of Gleaming Polish. "I bear grave news from the Crystal Empire."
"A crystal pony!" Spike and Twi gasped simultaneously. "What's happened? Is Cadance in Problem? Is Shiny is trouble? Are they both in trouble? Has the Empire melted? Is a meteor on a collision course? Is..."
Twilight continued to rattle off increasingly improbable disasters as Gleaming Polish struggled to maintain a pleasant expression. Spike merely leaned against a wall. "Don't worry, she'll stop to breathe sooner or later."
Finally, when Twilight was gasping for breath, Polish cut in before she could continue. "I am not privy to the full details of Princess Cadance's motives, but there is no apparent catastrophy in progress. She does, however, request that you depart as soon as possible."
"Alright, let me just round up the girls and we can catch the next train out. Spike, I need you to stay here and keep the library in shape..."
"Actually, Princess Cadance has requested his presence as well. She said that his actions during the defeat of Sombra make him critical in resolving the current difficulty." Polish cut in.
"Uh, alright then. You and Spike head over to the station, I'll round up the girls." As Twilight rushed out the door, Spike was facepalming.
"And she forgets to pack. As usual."
"I'll give your stuff Spike." Polish offered.
Spike's face brightened up with that. "Really? Thanks miss... I don't think we got your name."
"I am Gleaming Polish, Spike, and its no trouble." She replied as the two climbed up the stairs.
Once the packing was done, Polish loaded the bags onto her back and the two set off for the train station. "Oh man, I can't wait to finally go back to the Crystal Empire!" Spike exclaimed.
"Trust me, there are plenty of ponies who can't wait for you to be there."
Shortly before Gleaming Polish arrived at Twilight's door, Rainbow Dash was out practicing tricks near the Ghastly Gorge. Shortly after pulling off the Aerial Ace, a beginner level trick used to warm up, she caught sight of distant mare hanging precariously from the rocky cliffs. Rainbow rushed in to help, grabbing the mare and flying her to safety before he grip had even begun to loosen.
"Oh, thank you so much for saving me!" The mare swooned.
"Ah, don't mention it. Everypony's safe while RD is around. She set the would have been victim down and got a closer look at her. "Hey, you're a Crystal..."
Her next words were cut off by a stiff punch to the gut, the pony's weighted horseshoes, painted to blend in with her coat, knocking the wind out of the pro flier. The mare then threw a hoof down on Rainbow's shoulder, knocking the surprised pony down and vaulting her attacker over her. With Rainbow's face in the dirt, and her attacker's hind hooves planted firmly on her own back legs, the prismatic maned pony felt a jolt of pain crack down her back, followed by a numbness in her wing.
Rainbow Dash attempted to fire up her wings to rocket away, but her wings wouldn't respond to her commands. Her decades of practice fine tuning her physique suddenly failed her, as her efforts to activate her wings was met with only a dull ache.
Rainbow's focus on her wings was broken by a new, frightening site. Her eyes widened as masked, cloaked ponies from seemingly nowhere advanced on her...
Several minutes later, Rainbow lay beaten and bruised before the crowd of ponies, but her inner fire refused to go out, she limply swung her forehooves out at her attackers, too blinded by the blood in her eyes to see the attacks were useless.
One of her attackers removed a black, fractured crystal from his saddlebags and placed it against Rainbow's forehead. It began to glow with a soft light as the cracks filled in and Rainbow's eye rolled back in her head. The pony pocketed the now flawless crystal and turned to his comrades. "Damage the environment to replicate a crash, then return to the train. She will be discovered shortly."