As the two sisters flew over Canterlot, for the first time they saw, with their own eyes, the devastation that Grogar had caused. Whole buildings had been razed to the ground, their crumbling remains being trampled slowly by the undead hordes. Small groups of soldiers, knocking down the occasional undead as they made their way back to their bases, their heads turned to the ground, in mourning of the many friends and allies they’d lost over the past few years.
And in amongst the crumbling ruins, they saw familiar buildings, remnants of times long gone. The theatre where they’d seen their first performance… That bakery their mother had taken them to that one time, where Luna ended up covered in icing… But none of these shattered childhood memories could compare to what Celestia was about to see…
Right there, half-destroyed and almost beyond recognition below them, was the brick-lined building in which they had spent the majority of their lives: Queen Galaxia’s School for Gifted Unicorns. Upon seeing that familiar building ablaze, Celestia’s heart felt as if somepony had dropped a 100-pound weight on it. She closed her eyes, all the memories of her school life flooding back to her in an instant… She hated to think of the undead breaking down the doors, the teachers trying their best to protect themselves and their students, but ultimately failing as the children screamed and cried behind them…
“Tia…”
Celestia was once again brought out of her thought by Luna, who’d obviously seem her pained facial expression.
“Don’t worry, Tia… We WILL do this - we WILL defeat Grogar. And once we've done it, we’ll rebuild it. We’ll rebuild it all…”
Celestia was only slightly comforted by her sister’s words, but nevertheless she began to pick up the pace, propelling herself slightly faster in the direction of the Crystal Mountains.
The pair flew for what felt like an age. As the sun finished setting, the moon began slowly rising into the sky as the two sisters continued their exodus, their journey to finally defeat the one who had brought so much pain into their lives, and to their country. At the altitude they were at, it was cold and bitter, but still they continued on - they could never give up, lest Equestria fall into the clutches of an evil psychopath.
Seconds turned to minutes, and minutes turned to hours. Celestia was beginning to doubt her own judgement when another brilliant sight met her eyes… As they flew further, snow-covered peaks began to appear over the horizon, expanding into deep blue mountains, dotted by the occasional tree or outcrop of snow… These were the Crystal Mountains, their final destination… And where Equestria’s final fate would eventually be sealed.
“Now, we just need to find the entrance…” Celestia spoke for the first time since Canterlot. “You take this side, I’ll take the other.”
“I don’t think we’ll need to look…” Luna said slowly, indicating with her hoof as more of the mountains were revealed… In the mountainside, sticking out like a sore thumb on the backdrop that was the deep blue mountains, there was a cave, from which a bright orange light was emanating. Many dark figures were exiting the cave, and some were entering… Celestia immediately understood what Luna meant, and so the pair flew a little lower to confirm their suspicion.
As they thought - the dark figures leaving the cave moved clumsily, their mouths hanging open, deep gashes all around their bodies. Those entering the cave carried what looked like dead bodies on their backs, fresh from the battlefield. These were Grogar’s Undead… and this cave was their place of origin. Celestia almost took pity on the poor ponies, dragged out of this world so quickly… and just as quickly dragged back, hungry for pony flesh.
Eventually, the sisters reached the mountainside, and after finding a flat enough area, landed with a simultaneous flap of their wings. Looking down at the steady stream of undead slowly leaving the cave, they began to consider their plan of action. Luna began the conversation in a hushed voice.
“How do we get in?”
“Well, one way would be to blast our way in…”
“Two ponies, even alicorns, against a whole army of undead, plus Grogar, would be a recipe for disaster though… We've seen what they can do to whole armies…”
“True…”
The pair remained silent for a moment, before Celestia spoke again.
“We could.. hide behind some bushes?”
“And do what?”
“Sneak in, of course!”
“Do you see any bushes around here-- hold on!”
The idea of sneaking in gave Luna an idea. “Why don’t we disguise ourselves? Pretend to be zombies and just walk right through the door?”
“That sounds like a risky move, and it most likely won’t work... But now that I think about it, it may be our only way in…”
“Then let’s do it.”
So, Luna and Celestia carefully descended the mountain, being careful to stay out of the way of the undead, so they wouldn't notice the pair as they prepared their disguises.
“Now… disguises.” Luna said, in a hushed voice. “Hold still a sec, and shut your eyes…”
Celestia, trusting her sister’s judgement, did so, allowing Luna to do whatever she had planned. She felt a little funny as she felt Luna’s magic making little cosmetic changes to her body, but she remained still, and her eyes remained shut, waiting until Luna was done. Eventually, the strange sensation stopped.
“Aaand… open!”
Celestia opened her eyes, looked down at herself… and almost let out a large gasp, before she stopped herself.
It looked as if her body had been chopped to bits and cheaply put back together again. She had gashes all over her body, and her skin was a darker tone - even her mane felt heavier.
“They aren't real gashes - it’s just a cosmetic effect. I don’t know now many times I used it to scare kids a few years back…” Luna commented.
“I bet that caused some trauma...” Celestia said, half-sarcastically. She was still a little unnerved by her appearance...
Luna then performed the same spell on herself, and Celestia couldn't help but wince a little as she saw the fake lacerations slowly etch themselves onto her skin… it looked very painful.
Now very much satisfied that they looked sufficiently non-living, the two sisters kept to the shadows, slowly creeping towards the cave entrance.
Eventually, they drew close to the cave mouth. The two sisters held their breath and temporarily said goodbye to their sensible selves as they began lurching forwards into the steady stream of light, their breaths deliberately rattling and occasionally moaning a little as they attempted to emulate the undead surrounding them. To their luck, the creatures were as stupid as they looked, and didn't even bat an eyelid at the two sisters waltzing through the cave mouth, and they did not fail to drop this act as they stepped in. Once inside, however, it was hard not to. In fact, Celestia had to swallow a gasp when she saw what was inside…
The interior of the cave was smallish, with a side passage to the right of where Luna and Celestia were. Towards the back of the cave, there was a small elevation, leading up to what had been causing the orange light: Adjacent to the wall, there stood a great stone arch, inside which there was a great orange portal - the undead entering were throwing the bodies they were carrying into it, and the line exiting was made up of a combination of undead leaving after just having deposited a body, and newly reawakened undead, emerging from the portal.
Not taking much time to look at this, Celestia and Luna stumbled towards the side passage, assuming that Grogar must have been that way, and after they were sure that the undead couldn't hear or see them, they dropped their act.
Celestia, breathing a sigh of relief, spoke: “Well… That was stressful!”
Luna replied, equally relieved. “You can say that again!”
“Now… we find Grogar. Time to end this once and for all.”
With that, Celestia continued up the passage, which opened out into what seemed to be a long flight of spiral stairs. A VERY long flight of spiral stairs.
“How much longer?” Luna said, gasping for air as she climbed stair after stair…
Celestia wasn't faring much better, but nevertheless she replied “We’re almost… at the top…”
“Good!” Luna said in response, both the stairs and the wait driving her mental.
The pair climbed, and climbed, and climbed some more until eventually, Celestia stopped dead in her tracks.
“What’s wrong?” Luna asked, concerned.
Celestia’s reply was tentative and shaky. “We’re at the top… and whatever Grogar’s doing, I don’t like the look of it”
Looking round her sister, Luna saw exactly what she meant…
The top of the stairs opened up to a plateau, hidden from view by the surrounding peaks. Looking up, the moon seemed to shine brighter than ever from here… But this was not something that the sisters dwelled on, for what was actually on the plateau was what caught their eyes. There stood their arch nemesis, Grogar, standing over what seemed like an altar, muttering to himself. Behind him, there was another portal, but unlike the plane through which the undead were passing, this one was clear, and through it, one could see what looked like a vast fortress, the walls and spires of which looked twisted and warped, even malicious and evil.
“You like it?”
Celestia and Luna nearly jumped out of their still-disguised skins when they heard Grogar speaking directly to them.
“Don’t think I didn't see you there, waltzing through the entrance, thinking you were being all stealthy. I see EVERYTHING that enters and exits this cave.”
He turned away from the alter, which the sisters could now see was, in fact, a Pool of Surveillance, trained on the entrance to the cavern.
“You should be glad that my Shadow Warriors didn't notice you… though I must commend your effort… You certainly are clever little fillies…” Grogar walked over and patted Celestia gently on the head as he said this, angering Celestia greatly.
“Get behind the wall, Luna.” Celestia muttered to her sister.
“But…”
“Do you remember what I said back at the palace? Nopony else is dying for me. This is something I have to do alone.”
Understanding, but still concerned, Luna backed around the corner and listened as Celestia confronted the evil madman.
“It’s over, Grogar! This little vendetta of yours has gone too far! Stop this at once or I WILL destroy you!” Celestia knew full well that her threat was empty, but she didn't falter. She couldn't show weakness, not now.
“A vendetta?” Grogar suddenly shouted in reply. “Hah! You think that this whole war, the whole reason I created this army, was for revenge? Maybe you aren't so clever after all…”
“...What?”
Celestia’s heart began beating faster. What did Grogar have planned?
“Well, you see, before killing your oh-so-dear mother, I had an idea… Why stop with your mother? Why not bring down the entire Equestrian Empire with it? And that idea brought me here - to the Crystal Mountains, where I was able to operate freely, without fear of being seen or discovered. One by one, I killed more and more alicorns, binding their spirits, past and present, to my will, eventually gaining enough power to… well, it’d be better to show you myself.”
Before Celestia could answer, Grogar threw his head to the sky, and unleashed a beam of light from his horn. The beam travelled through the air, before finally hitting its final target: The moon.