As soon as the castle appeared, Starlight Glimmer was teleported to it as if summoned, leaving the Knights without a target. They looked at the gigantic watery construct in amazement.
"What does she even want that thing for?" Spike said what they were all thinking.
Before anypony could reply, the group was once again astonished upon seeing the castle begin to move. It wasn't moving very fast, but having such a huge thing move at all was already quite impressive.
"It's going toward the middle of Equestria." Scootaloo judged "It's not headed straight for Canterlot, but it is gonna go over most of the kingdom."
"We should meet back with Princess Luna and discuss our next course of action." Applebloom said
The others agreed, so a few seconds later the whole group was off in a teleportation.
+0+
They reappeared in the air close to the point where they had met up with Luna at first. The princess was flying nearby, so she immediately noticed their arrival and moved to them.
"What's the situation?"
"We were unable to prevent Starlight from completing the ritual. Now she has a giant water castle moving toward here." Spike summed things up.
"Really?" Luna replied, then used a spell to increase her sight and look in the direction he had pointed "Oh yeah, that sure is a giant water castle... It's not moving that fast, but is it just me or is the castle accelerating?"
"Accelerating?" Scootaloo quickly used a spell of her own to check "Oh yeah, it is definitely moving faster than when it started."
"That's probably not good." Sweetie Belle said.
Right after that, a message spell reached Princess Luna, who took a momento to read it before turning to the Knights.
"It's even worse than it seems. The effect is a little too broad for us to perceive it easily, but apparently the appearance of that castle is altering the climate on a large scale." She explained the contents "My sister has mobilized every single weather team to fight against that influence, but if the castle keeps getting closer, that's going to become increasingly untenable."
"Then we really need to stop that thing." Spike summed up the situation.
There was no disagreement on that subject, so the next step was figuring out how exactly they'd do that.
"First things first, is there any way of hijacking control of the ritual energy or forcing it to disperse?" The Princess asked.
"Very unlikely." Was Scootaloo's opinion "Starlight Glimmer has showed phenomenal understanding of ritual magic, doing things like using spells as ritual steps and conducting the ritual at a distance. Her magical control is also at a genius level. I'm sure she did her best to remove any weaknesses she could from the ritual as she was designing it, and also prepared numerous countermeasures." She sighed "Trying to disrupt her ritual magic would require acquiring deep knowledge of its mechanics plus a ridiculous level of magical ability to deal with her counter-measures and her own interference on the attempt.
"Or far more magical power than we have access to. Or some trump cards that could help out with the other requirements." She added after a moment.
"So it's not really a reasonable plan, then." Luna replied "So the other option would be finding a way to attack Starlight Glimmer herself."
"That's gonna be pretty difficult, considering she's now inside that water castle." Spike said "We'd need to deal with whatever defenses she set up there while also fighting in an absolute home field disadvantage."
"Yeah, that would be difficult, but there's a way to give you a higher chance." Princess Luna spoke with a smile.
"Really? What do you propose?" Applebloom asked.
"We'll do a two-pronged assault." Luna replied "You Knights will infiltrate the castle and hunt down Starlight while I'll battle the castle from the outside to slow it down and force Starlight to split her focus."
"Really? You're going to fight as well, Princess?" Spike was surprised.
Equestria's general policy was to avoid having the alicorns involve themselves directly in such crises if it was not necessary. That was due to three factors: One was the utility of having them holding down the fort to prevent incursions into the heart of the realm, which was also a territory that gave them a great advantage due to special preparations and mechanisms developed over the eras. Two was the fact that their indirect support was often more valuable than any contributions they could have made in person. Three and perhaps most important was the danger inherent to putting the powerful alicorns in the line of fire.
Fighting would inevitably cause them to be weakened, which could allow opportunist villains to take advantage. Sombra's feat of taking control of Luna hadn't been because of that, but it was an example of what could happen if the alicorns weren't careful. And that was far from the most dangerous result that could arise. Villains with more ambition than sense could try to exploit an alicorn's connection with their source of power, and the possible results of messing around with astral bodies (in the case of Celestia and Luna) could be catastrophic.
"Yeah. We're a little bit shorthanded, plus this is a good opportunity." She replied "I can call upon guard pegasi to keep watch over the surroundings and prevent any villain from trying to sneak up on me, Starlight's ritual disturbed the surrounding magic enough that I'm not worried about traps planted beforehand, plus the open sea is a very difficult place for enacting such plots anyway." Luna explained her reasoning.
"Hmm... Yeah, now that I think about it, that's probably fine." Applebloom said after thinking for a few moments "Specially if we manage to deal with Starlight quickly."
"We should go all out, then." Sweetie said "It should give us the best chance of doing that, and I know we can maintain the Triple Bond for long enough now."
The other two Crusaders looked at her in surprise but then nodded. They had trained for that, and now was as good a time as any to show the results of their efforts.
"In that case, I'll wait until we meet Starlight before going all out myself." Spike said "I'll support you three during our break-in, but you're the ones who will have to do the heavy lifting to get us there."
The trio agreed with that. But there was still one more question to be answered, a question Scootaloo was the one to ask:
"But how do we actually get inside the castle?" It was a pertinent question, since Starlight's water construct castle looked like a fortress version of Canterlot Castle, except without windows or any other openings one could use to go inside "Do we set up a Triple Bond to help with that?"
"That won't be necessary." Princess Luna said "I can create an entry point for you."
+0+
After the princess' assertion, the Crusaders took a few more seconds to decide on the best combination of bonds for their castle infiltration. Eventually they settled on Shining Armor's (for the defense magic), Rainbow Dash's (for speed and power) and Applejack's (for perception). The weakness of such a combination was long range attacks, so Spike shifted his body to sprout dozens what looked like crystal spikes on his back. That was a physical feature of the crystal dragons, who could use said spikes as very powerful amplifiers/focuses for magic. Shifted like that, Spike essentially became a dragon-shaped magical artillery piece.
As expected, his mobility wasn't that great when shifted in such a way, but the Crusaders could give him a boost via magically enhanced tailwind, so that wasn't a problem. And with everything settled, the group flew towards the approaching castle, and when they were three quarters of the way there, the Crusaders finally put the plan into practice.
"Triple Bond!" The trio declared, a cutie mark appearing over each of them.
Their flying platform expanded and englobed them as their power was unleashed. The energy of the sphere became a pure white and the air around them heated up simply from the comparatively minor amount of energy that was leaking due to their still not quite perfect control of that technique. Then two cylinders of energy erupted from the sides of the sphere, starting out completely nondescript but quickly morphing into the shape of two majestic wings. Following that, more energy sprouted from the top and bottom of the sphere, which formed a birdlike head and two clawed legs, respectively.
The entire body became more and more detailed, revealing the bird to look mostly like an eagle, but the eyes were a little bit bigger, and they looked almost more real than everything else, with a piercing gaze that seemed able to see through anything. And then finally, one last transformation took place, as the bird became clad in knightly armor, looking like it was ready to march through even the deadliest battlefields.
With that done, it was time for Princess Luna to do her part, so she took off flying straight up, quickly breaking the sound barrier as she ascended. Soon enough she reached a point that was deemed high enough and then she began a dive that also broke the sound barrier pretty early on. The alicorn didn't push too much as she descended, so her speed didn't keep rising, but instead Luna began focusing magical power into her own body, preparing for her strike, reaching a point where the density of energy was warping space around her and still increasing.
Then, mere moments before impact, the princess declared her spell:
"Astral Magic: Moonfall!"
And the instant she hit, the magic triggered, causing Luna to embody the mass of the moon for a fraction of a fraction of a second. The first layer of water she hit experienced pressure equivalent to being hit with a supersonic moon, an astral body heavy enough for scientific notation to be required in order to clearly denote its weight. It didn't even have time to vaporize as it was broken down at a molecular level, while the second layer was knocked away hard enough to briefly reach a small fraction of the speed of light before it crashed against the rest of the water around and broke open a large hole on the castle's front wall.
Even the sheer amount of magic Luna had focused wasn't enough to embody the moon for longer than the absurdly small amount of time she did, which was exactly as planned, because otherwise the impact would have resulted in the entire continent being devastated.
Still, it was an incredibly brutal crash that not only stopped the castle's already significant forward momentum, but even made it slide backwards for a little bit. It also resulted in Princess Luna becoming dazed, but she had done her part and opened the path for the Knights to advance.
'Whoa.' Thought Spike as he and the Crusaders flew into the hole in the castle's wall. The three fillies were having similar thoughts, of course.
Then they were in, so the four Knights turned their focus to the mission, and their surroundings. They were inside a large, well-decorated hall, which would seem to belong to an ordinary castle were it not for the fact that everything in it was made of water. It seemed to be some sort of entranceway, being a large open space dotted with statues and having a large doorway on the far end.
Looking up they could see that the hole they had used to get inside was already quickly closing, but soon the group had other things to worry about, namely the statues, which had come to life and began attacking, some with long range spells that used water or ice and other by rushing the Knights, manifesting weapons as they went.
"We can't get bogged down fighting those things." Applebloom said as Spike used powerful fire spells to intercept the enemies' ranged attacks "Let's rush through."
The others nodded in agreement, and so their bird manifestation flapped its arms, instantly accelerating to half the speed of sound and crashing through the approaching line of statues, Spike at its back. They soon got too close to the spellcasting enemies for Spike to intercept all their attacks, but they instantly created two layers of barriers that managed to completely nullify the enemies' spells, allowing them to pass unscathed.
Still, they hadn't reached the end of the hall yet, so there were still quite a few statues ahead, and the castle itself (or more likely Starlight Glimmer) seemed to be responding to their efforts by molding more and more statues to harden the opposition, which was being done fast enough to match the great speed the Knights were moving at.
The Crusaders made barriers after barriers to protect themselves from the overwhelming attack, while also using their speed to to dodge around the wide area, searching for the path with the least opposition. At the same time, Spike continued to launch powerful magic, both intercepting big masses of enemy offense as well as thinning their numbers.
Still, even with all that, the numberless masses of enemies constantly spawning were getting to be too much. The four Knights knew that slowing down would just mean getting completely overwhelmed and forced to pull out something big in order to escape, but it was getting to the point where they just didn't have any choice.
So it was a good thing that suddenly an explosive noise was heard and the enemy resistance dropped a noticeable amount all at once.
'Must be Princess Luna's doing.' Scootaloo thought, realizing that Starlight Glimmer was now having to devote a larger portion of the castle's energies to the fight against the alicorn, thus making things easier for them.
The Knights wouldn't waste that chance. With one last push, they reached the end of the hall and broke through the heavy doors into the next part of the castle.
+0+
Luna hadn't taken all that long to recover from the effects of her previous spell, it was just that the Crusaders were moving so fast that they had already gone a long way during that short amount of time.
As soon as she recovered, the princess resumed the battle. Her first strike was a quick moonbeam, but the castle retaliated fast enough it was obvious that the response was automatic, as a thick water spray shot from the area Luna had been targetting, the water droplets diffusing the beam into uselessness.
'So this thing has very good defenses against light attacks. In that case...' Luna thought, before launching herself at one of the towers and declaring "Crescent Blade!" as she slashed with her right forehoof, manifesting a gigantic lunar crescent that clashed against the castle tower, which shaped its side into a spear point in order to deflect that attack. Then another tower stretched itself above the princess and swung down onto her like a pendulum, hundreds of tons of water moving at great speed.
"Waning Slash!" Luna declared in response, slashing downwards with both forehooves and striking the watery construct from above with a shadowed moon apparition that manifested itself above the tower, far away from the attack's supposed origin, and struck with sufficient force to misdirect the swing away from the alicorn. That attack was dodged, but the tower Luna had first attacked rallied, stabbing towards the princess while the castle walls unloaded a barrage of hundreds of fish shaped magical missiles.
"Mythril Barrier." Luna spoke, manifesting a silvery substance from her armor that quickly grew to the same scale as one of the towers and formed a barrier that stopped the stab, then a follow-up declaration of "Dark Manifestation!" resulted in the creation of a shadowy substance that spread into countless tendrils, reaching towards and knocking away the missiles. Then the falling tower shaped itself into an axe-like structure and swung sideways towards Luna, forcing her into using another crescent blade spell to deflect it.
But at that point the alicorn decided to take back the initiative and shaped her mythril barrier into a gigantic hoof that bucked the castle's wall and forced it to divert magic power into repair. She pressed the advantage by turning her dark tendrils into a giant mace and smacking it into the castle, creating a hole that was quickly patched up.
Then the air itself froze, or rather the water on it did, as the castle counter-attacked with an instant wave of cold that would have trapped Luna inside a block of ice.
"Woah, that was close." She said.
It would have done that, had she not abandoned both of her constructs and dashed away at extreme speed, briefly turning into a shadow to avoid the air resistance. Still, Luna wasn't discouraged by the close call. Much to the contrary.
"Hehehe, it's been a while since I've fought seriously. This is fun!" She spoke, before diving right back into the battle.
+0+
After crossing the doors, the Crusaders and Spike found themselves in a formation of corridors shaped like a square. A quick scouting spell by Scootaloo revealed that said square surrounded a center area that held Starlight Glimmer, and that there was an opening on the opposite side from where they were that led into that area.
"Is it a trap?" Asked Spike.
"Should we just blow through the wall to reach her?" Sweetie Belle suggested.
Scootaloo thought for a few moments and then replied "No. She's using a deliberate opening to take advantage of the magical laws regarding openings and exits."
"Ah, so by deliberately creating a path towards herself, she can make alternate paths like through the walls way harder." Applebloom got it.
"Yeah. I think we'd still be able to get through with sufficient effort, but that would probably exhaust us." Scootaloo said.
"And why isn't she attacking us right now?" Spike questioned.
"I think... We're a bit too close to the entrance hall." Scootaloo deduced "The way her magic works seems to involve different flows of magic for different places. I can feel her manipulating magic to set up defenses along the corridors, but apparently there's too much interference to do anything here."
"We should charge forward, then." Applebloom said "No sense letting her have too much preparation time."
The others agreed, and then the group flew through the corridor heading left, managing to reach the first turn before encountering the next bit of resistance. That resistance came first in the form of the water chandeliers on the ceiling, some of which dropped down like sharp implements while others began to fire projectiles and beams at them.
Using brief bursts of wind magic to boost themselves around, the Knights managed to dodge the falling chandeliers, even as they began to twist and stretch in order to increase their range, while a series of barriers handled the projectiles. But only a few seconds into that and things got more intense, as the floor of the castle began to attack as well, having a water carpet separate from it and shift itself into a series of barriers and agressive objects like spears and spikes, all the while projectiles were also being fired from below.
Spike had to join in on the defense, using artillery spells both to intercept projectiles as well as destroying obstacles, the crystals on his form humming as they channeled large amounts of magic power into his offense. The attacks they were suffering just kept getting heavier and heavier as they went, though, until Applebloom was forced to utilize the perception inherited from Applejack's cutie mark to see the flows of magic on the castle and predict their attacks, thus being able to utilize movement and quick interception spells to significantly blunt the enemy offense.
Doing that was an added drain on their bodies and minds, though, which was why they didn't do so at first, but at that point it was worth it to force their way through. Still, even that failed to be enough when the group turned the corner before the final bit of corridor they had to go through to reach the entrance to the center and the walls started attacking as well.
It was absolute and utter chaos as bullets of ice and water came from every dirrection, objects stretched and contorted as they reached for the Knights and numerous layers of barriers completely stopped their advance short, forcing them to move back in order to not get overwhelmed.
"Tch. This is tough." Scootaloo noted.
"Okay, we're gonna need something big to get past this, so let me do it." Spike said.
"Are you sure?" Applebloom asked.
"Yeah. This is gonna wipe me out for a bit, so you'll have to fight Starlight by yourselves at first, but I still think that's the best option."
"Then let's do it." Sweetie said, speaking for the trio.
"Just give me a few seconds." Spike said and stopped firing in order to charge an attack.
The pressure of the castle's relentless attacks was far greater without the dragon's support, but they were not trying to move forward at all, which helped. The Crusaders used every single trick their current form had in store: The weather manipulation and speed from Rainbow Dash's cutie mark, an endless supply of shields from Shining Armor's and the predictive perception from Applejack's.
They dashed from side to side to reach better positions, broke through what they couldn't dodge with powerful spells and blocked everything else with shields. They were pushing themselves hard, but they only needed to hold on for a few seconds.
They could do it. And thus, the dragon had all the time he needed to charge up his attack.
"Dragon Fireworks!" He declared after the seconds had passed, unleashing the biggest burst of magic he had ever shown on any mission.
And the magical crystals dotting his current form ejected themselves, shooting into the last corridor like rockets. Spike grunted in pain from this terrifying act, but one couldn't argue with the results. The crystals shot through the air and passed through any obstacles or barriers in their way like they weren't even there, by the simple measure of overwhelming power, and the countless shots that were fired against them failed to even slow the crystals down either.
Then they exploded with extreme violence, unleashing power that could have easily annihilated a mountain the size of the water castle, but the power was concentrated entirely within the corridor.
The result was that the multitude of defenses that the water castle had placed in the path of the Knights was completely annihilated, leaving only a bare water corridor behind.
Spike quickly shifted back into normal form to heal the open wounds that were the result of unleashing the crystals, and one could easily tell that he was very drained from that act. But he had done his job, and the Crusaders did not miss their chance. They flew through the rest of the corridor while still carrying him, and dove through the opening to the center room.
The final confrontation with Starlight Glimmer awaited.