The Princess of Love and the Princess of the Sun eventually arrived at the recently revamped Vault of the Elements. After Discord had breached her previous model at the Canterlot Tower, Princess Celestia had listened to her sister's suggestions, and made many improvements. Not just magically, but physically as well. The Canterlot Tower had been a beautiful location, but the Vault lacked its weaknesses. Such as windows. Celestia was certain that if Queen Chrysalis had not influenced the Royal Guard, the front doors would had never fallen.
As it was, the small courtyard abutting the entrance was vacant. The guard roster being short due to injuries, to both body and mind, its inner strongroom's security spells had been determined adequate enough to keep the content safe without Pony presence. Thus the four Ponies approached the grand entrance unimpeded, the two guards staying the ceremonial two body lengths behind the charge as they walked up the short flight of stairs.
Princess Celestia used a forehoof to open the massive doors, explaining with some pride how she herself had designed them to resist magical forces This revealed a large dark chamber. Only a sheen glistening to the left could be seen within, along with an odd grassy odor.
"Hmm, the lighting conduits must have been damaged in the attack," remarked Celestia offhoofedly as she entered, immediately lighting her horn with a glow spell. As she did this, they were all confused by what was illuminated. The right side of the inner chamber was just as it had been when the Elements had been entrusted to it. The light purple and pink stone columns flanking the murals that replicated the stained glass of Canterlot Tower, then ascended far above to the elegant vaulted ceiling. The tapestries there hanging, more symbolic than descriptive, yet tasteful all the same.
As their gaze was drawn to the left, a sense of confusion was shared by all. From the molding at the height of the wall, coating the wall entire, to a gloopy accumulation at the floors edge, was a strange viscous substance.
The light from Celestia's horn made it seem to be clear, yet infused with small flecks throughout. The flecks adding an attractive sparkle to the near opalescent reflected glow from the illuminating spell, as if reminiscent of an expensive potter's glaze.
Cadance walked over to the left wall, where she could make out that the flecks were actually two colors. With a greenish/turquoise that accented the more numerous black pieces. None of these seemed to be larger than a daisy petal. Sniffing, she confirmed that the material was definitely the origin of the mild grassy scent the permeated the area, "Do you think this is some kind of secretion left by the Changelings?" She took a step back at the idea, "Do you think it is safe to be in here Auntie?"
Celestia approached her niece as she went to get a closer look as well, casting an identification spell as she inspected the gloop. Sad resignation encompassed her features as she received the spells results, speaking softly, "There is no need to be afraid of this, Cadance. The Changelings did not place this here. Rather, this seems to be the remains of the Changelings themselves."
A loud, moist, plop punctuated her statement, as some of the glistening semi-fluid fell from the ceiling into the growing syrupy puddle. Horror dawned across Cadance's muzzle, "What . . . but, how.. how could this be the Changelings?"
Celestia glanced up to look at where the wet line began, and thought about what was in the opposite direction. Her eyes widened at the realization, "Cadance," she spoke softly, "I believe that this is the result of the shield spell that you and Shining Armor released. We saw how Queen Chrysalis was launched by the shield. Here there was no path for them to be moved, so the bubble pushed them against the wall until, well, until they were no longer considered a threat by the spell."
"But, this is just goo," Cadance's voice trembled as she backed towards the door, "This couldn't have been Ponies!" She insisted.
The carnage affecting even her composure, Princess Celestia fell back to lecture mode by reflex, "It seems that Changelings are closer to insects then to Ponies, anatomically at least. Beneath their hard black shells they don't have blood and tissue as we do. Rather they have this goo, which lets them move similar to how hydraulics work. Anything that's softer than their exoskeleton must have been liquefied by the crushing power of the force field expanding." Only now did she look up from the scene and over to her niece. Just in time to see her bolt out of the doors, and to the side of the stairs.
Realizing now the impact of the carnage that had been revealed, Celestia quickly trotted over to the vault door, released the spells that sealed it shut, and retrieved the Element of Kindness from within. Then, just as quickly, she resecured the vault and joined the other three ponies outside. Shining Armors guards, while a bit green around the muzzle, we're trying to support Princess Cadance while she tossed her cookies. And apple fritters. And wedding cake.
Princess Celestia addressed them, "Guard Bright, go immediately to the senior cleaning staff's office. Tell Mr. Span that there is a code 84-b at the Vault of the Elements. Then immediately return here and ensure that they work undisturbed. Guard Stone, head to Captain Moonglow in the Lunar barracks, inform him of what happened, and that he needs to investigate any buildings near the castle where the force field could have similarly trapped other combatants. She is to look for traces like what happened here. Any locations discovered, have him relate to myself and Mr. Span. Neither of you are to tell anypony else any details of what you have seen or heard here today." At their frozen forms she added, "Go. I will care for Princess Cadance." At this reassurance, they finally took their leave.
After a couple of minutes of Celestia resting her wing over Cadance's dry-heaving form, the Princess of Love started to calm enough to speak, "How could our love have done that?" She wiped her muzzle with a wing, "I only wanted them to leave us alone. Not to do that to them." Her eyes got even wetter, the tears now flowing freely.
Celestia drew her niece closer with her large wing, "I know Caddy, I know. But that was powerful and unique magic. The two of you had no way to know what might have happened, even had you the luxury of time to think about it. You were desperate, and as a result of your actions the pair of you saved all of Equestria. I know it may sound callous coming from this old mare, but the reality is that it was us or them." She then hugged the smaller Alicorn tightly, "As regrettable as it is that this was a consequence, your actions are why your loved ones, as well as all of Canterlot, are free tonight. The reason that I am not still imprisoned inside of that cocoon." She sighed, "Yes, you should always grieve for the enemies that you could not save, but please, do not forget to rejoice in the lives of all of those that you did save."
Cadance looked up at the mare who was like a second adoptive mother to her, blinking the tears out of her eyes, "I think I need Shiny. . . I need to hold Shiny right now."
Nodding, Celestia guided her back to her feet, and the two began walking back to the main palace. Cadence oblivious, as a small group of cleaning staff led by Guard Bight passed them, headed to the source of their mutual discomfort. Nor did Cadance register when Celestia gave some quick words to the head of the crew. In fact Cadance did not register much of anything as they traveled. Not until she felt familiar hooves wrap around her did she rouse from her catatonia.
She then realized that she was now in a private study, along with Princess Celestia, Princess Luna, and most importantly, her husband. Into whose warm embrace she released herself fully.
Princess Luna released the flow of mana from her horn, "There, sister, we are secure from curious ears. Now tell us what occurred to make you so grim. Do you have news of other victims of the Changelings?"
Celestia sighed, "Victims, yes. But not of the Changelings." She then related what they had observed in the vault, as well as her deductions about what had caused it. She had expectations for Prince Shining Armor's reaction, but mirth was not among them.
"Ha!" He blurted, "At least some of that filth didn't get away scott free."
At this even Luna's eyebrow was raised, "Defeating an enemy in honorable battle is one thing, Captain, but indiscriminate killing is not something to revel in."
Cadance looked at her husband's face, distracted as she said, "They weren't just killed. They were liquefied! Who knows how many of them. All just mangled into one huge soup of offal." Her eyes closed, then quickly opened to escape the image seared into her mind, "No way to tell the remains apart, nothing for their loved ones to bury."
Shining Armor scoffed dismissively, "As if those creatures could form bonds. You heard Princess Celestia, they were bugs, not Ponies. And bugs deserve to be crushed."
Cadance couldn't believe what he was saying, "You can't mean that Shiny? Everything deserves to live. I certainly have legitimate reasons to dislike them for what they have done to me. To us. But they deserved better than that."
Shining Armor pulled away from her, and looked askance at her, "Apparently we are of different minds on this subject." He turned to the stunned Diarchs, "Forgive me Princesses, but I must take my leave and check in with the security details. I'll see you later Cadance." With that cool farewell, he departed the three stunned mares and closed the door behind him as he left.