~Sombra~
Even with three of Equestria's princesses going into battle, it was a daunting task to face. Even without the fact that damaging his enemy meant harm to himself, his mirror counterpart radiated incredible power - the energy bleeding off him easily rivaled Celestia. It began, as most battles between Unicorns did; with an exchange of magical blasts from all participants. Golden yellow, dark blue and sky blue from the princesses' horns - and of course sickening green and red from his counterpart. Sombra mostly watched and waited - hoping for a moment to contribute- though amid the flickering lights, raining blasts and explosions caused by their attacks, it became difficult to keep up with who was doing what. Even without the chaos, it was hard to really call this a fight. More of a struggle to actually hit their enemy.
There was little sense of "side" to the battle, even though it was four against one. The fact that Mirror-Sombra was a master at teleporting meant he could simply blink out as soon as they targeted him - frequently incinerating the area where he stood moments before - and then blinked back in some distance away. From the cruel grin on his face and the fact he had not yet made a move to counter showed that he was toying with them. That all changed though when Celestia and Luna joined horns and fired a single, concentrated beam of dazzling radiance - one that destroyed everything it touched and left scorch marks in its wake.
Snarling like a beast, Mirror-Sombra invoked a spell - and moments later, a wall of black spikes erupted from the ground on all sides - nearly impaling the royal sisters - who scattered and took flight in response.
Amore stepped up and fired another blast - the energy beam taking the form of a heart. Just before it impacted, Mirror-Sombra invoked a shield spell - and the two energies clashed with thunderous impact - scattering excess energy and debris every which way - as lethal as shrapnel.
Seeing a chance while his foe was distracted, Sombra lowered his head and galloped forward, snatching up a piece of that shrapnel in the process with his telekinesis. When he was in range, he redirected it - aiming to hit his counterpart in the side. Before he could do so, however, a black bladed scythe was conjured and sheared the rock in half. Behind it stood his mirror-self, grinning wickedly as he brought it back around in an arc - aiming the blade at Amore.
Without thinking, Sombra fired a beam of his own - disintegrating the scythe in mid swing.
"Leave them alone." He growled. "Your fight is with me."
"Very well." The other Sombra said, forming a replacement scythe from his shadowy aura. "Let us see what you're made of, betrayer."
"Do you have any idea..." Sombra growled, conjuring a blue shaded sword from his own magic. "...how sick I am..." a few test swings and he was ready. "...of you calling me that?"
The two stallions circled each other like sharks, both sets of eyes filled with hatred. Before anypony could blink, the duel was on. Magical blades met in a shower of sparks - sword and scythe interlocked and the blunt sound of grinding steel filled the chamber. In midair, their weapons ground to a trembling halt. On the ground, both stallions grunted with effort - sweat dewing their faces as the stalemate continued.
With a sudden grunt of effort, Sombra pushed his foe back - though his counterpart recovered - brought his scythe back around and charged. The true Sombra rushed forward to meet him - and thus began the second, much more brutal stage of the fight.
The princesses watched, astonished as the duel unfolded. While Mirror-Sombra was fast and aggressive, he was also sly and teleported around the chamber. His main self countered him blow-for-blow; anticipating his movements and striking back with a ferocity that could only come from a stallion that stood to lose everything. And there were other ways to fight that didn't involve swords or scythes - loose fragments of rock, even the ice crystals surrounding them were torn from their foundations and fired as projectiles. At one point, Mirror-Sombra simply resorted to ripping off chunks of the ceiling and hurling them at his foe. The true Sombra stood his ground - slashing apart every piece with his sword or blasting them into fragments with his magic.
With that, he lunged - aiming a stab right for his foe's shoulder. The scythe came back around in a well executed parry - followed by a riposte. The true Sombra retreated several steps, then brought his blade back in. Again, the scythe countered it.
"Fighting me is useless." Mirror-Sombra called over the din of strikes and parries. "If I die, you will die with me."
"I have prepared myself for that." The true Sombra retorted, a determined look on his face. "If it means my wife and son remain safe. Anything to protect them!"
"You mean to say you would sacrifice both our lives that your family might live?" His counterpart sneered. "Since when have you ever cared for any other than yourself?"
"Since the day I met Radiant Hope." Sombra countered. Another step, followed by another downward strike. A piece of Mirror-Sombra's cape fell, smoking to the ground. "Since the day Midnight Shard was born. I would give anything, pay any price to save my family." Sombra interrupted by lunged forward - grabbing his foe by the shoulders. His hooves wrapped tightly around his counterpart. For several minutes they grappled - pushing against each other. While they struggled, Sombra reared his head back and brought it forward - smashing his face against his foe's in a brutal headbutt. Both recoiled in mutual pain. Despite their shared agony, they hung on - neither backing down an inch.
"I shall not be denied!" Mirror-Sombra cried - forcing his head down - though from his aim, he did not intend to hurt Sombra - (and himself by extension) - but rather the princesses. Dark Magic burned from his horn as he charged a spell.
"Oh no, you don't. I'm dragging you straight to Tartarus with me!" The true Sombra shouted, forcing his own horn into his foe's path. His blue aura sparked and surged against the mirror-being - matching it.
"Sombra, no!" Celestia cried, though it was impossible to tell which of the two she called out for.
Even before the counterspell was finished, the ground beneath their hooves rumbled and shuddered. A ball of swirling energy crackled above the stallions - violently quaking as their energies crossed. The whole chamber was suddenly filled with blinding illumination as the ball split - and a massive explosion boomed - forcing the two away from each other - until they hit the opposite walls, simultaneously.
Mirror-Sombra was the first to rise - weakly, to his hooves. His cape and armor had been torn to shreds in the explosion - but it was his horn that appeared to have suffered the most damage: It had been cracked and blackened at the tip.
"This is far from over." He paused with a hacking cough. "...If you only knew what horrors await... you would not fight me. Don't you understand what I am trying to do?"
"We understand perfectly!" Luna cried. "We were not so different than you, once before: As Nightmare Moon, we caused Our subjects much grief - believing that eternal night twould be best for all - but we, like you were very mistaken!"
"The world you are trying to create - any world of yours..." Celestia joined in, her horn glowing brilliant gold. "-Would be a world without choice - without free will - or friendship or harmony!"
"That is why we fight you." Amore said, helping Sombra to his hooves. "To ensure that such a world never comes to pass!"
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~Twilight~
The Princess of Friendship could not believe her eyes. One minute she was confronting her former friend, the fallen Mirror-Sombra, the next she was face-to-face with a mirror image of herself, except the other Twilight did not have Alicorn wings. Seeing this, she went on the attack from the air - blasting at her foe with every spell in her repertoire. Only after the first barrage did she discover that even without wings, the other Twilight seemed to be as equally powerful as the Princess herself. Her counterpart teleported around the room or blocked each move with shields. Her last shot however, fired after a feint - hit home - right in between her foe's eyes. The blast burned into her face - searing part of it just above the left cheek. The opposite Twilight cried out in pain and rage - impotently looking at her with hate filled eyes.
To the true Twilight's surprise, there was no burning sensation on her own face. The damage done was not quite the same as it would have done to Mirror-Sombra. Perhaps he had not summoned their opposite selves to combat them, but had instead simply created shadow doubles to distract them.
Elsewhere in the cave, from the corner of her eyes she made out scenes of individual combats raging between the other element-bearers and their shadow-selves as well: Two Rainbow Dashes fought in the air; colliding into each other at supersonic speed with massive, rainbow colored shockwaves erupting with every impact. On the ground, Applejack fought another version of herself - one without a hat, alternating between kicks and wrestling on the ground.
Elsewhere, Pinkie was fighting another, flat-maned Pinkie with... streamers? And a rubber chicken? And was that a balloon sword she pulled out from... somewhere?
Bemused, Twilight looked further along and beheld Rarity having what appeared to be a fashion showoff with another, much more gaudily dressed version of herself.
Last but not least, there were two of Fluttershy having a stare-down. Neither had budged an inch - likely because they were unwilling to resort to violence - and so they were just as much locked in a stalemate as the rest.
Rather than press her advantage, Twilight turned to her friends and magically amplified her voice.
"Listen up! We can't beat our own shadow doubles, but that's why we're a team!"
Before Twilight knew it, she felt a sharp pain in her back and fell, hard onto the stone floor.
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~Applejack~
The apple farmer had heard the princess' shout - only to witness her get struck by a stray magical blast fired from her counterpart. Applejack turned back to her own foe. Like her, the Applejack she was fighting was strong, quick and used bucking kicks - not unlike how she harvested apples on her farm. Yet, for all their strength, neither was a trained fighter like Rainbow Dash or a Magic slinging Unicorn. They were simply two Earth Ponies going at it like street fighters, but each blow sent the other reeling.
It was at that moment that Applejack understood what Twilight meant. Turning away from her adversary, she galloped on through the melee until she reached her target - the opposite Rarity. With that, Applejack reached inside her hat and pulled a length of rope from it. After a few twists, she gripped the newly formed lasso in between her teeth and sent it flying - up and over the shadow-pony like a wrangler. Applejack then jerked hard and pulled her, digging both hooves into the ground behind her - sending the shadow counterpart flying.
Shadow-Rarity went flying, right in between a stray spell fired by Shadow-Twilight, disintegrating both her and the tacky brown dress she wore in a puff of smoke. With that, Applejack flashed a nod at Rarity.
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~Rarity~
Now that she was free of the hideously clad version of herself, the fashionista turned over to the next of her struggling friends - Rainbow Dash, still bucking and flailing wildly at her counterpart in midair. An idea formed in Rarity's mind - and with a quick levitation spell, she aimed at Shadow-Dash. Her aim was true - as the shadow-pony was too focused on her foe to avoid it. A moment later and the dark Pegasus was suddenly clad in a brightly colored gown - one not unlike her mane, though considerably more frilly. It was amusing to see the scowl form on the normally tomboyish Pegasus.
In midair, the true Rainbow Dash gave her a salute - then slammed her distracted counterpart with both hooves into the ground. Like Rarity's, the double vanished into black smoke.
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~Rainbow Dash~
The Pegasus turned her head towards the next foe in her path - Fluttershy. Dash made a mental note to give thanks to Rarity for helping her prove once again that she was the coolest Pony around. No imposter was going to take her down, especially when her friends were around. With that in mind, Rainbow Dash flew down in an arc at Shadow-Fluttershy, gaining speed as she did so. The first kick she sent straight in between her eyes - followed by a rising upper-kick to her lower jaw. Given her timid nature and abhorrence of violence, the opposite Fluttershy was hard-pressed to retaliate. Any blows she did attempt were soft, gentle kicks and attempts at wrestling with her. Probably from years of acupuncture and massage therapy - good for animal treatment, though not well suited for combat.
With a final flourish, Rainbow Dash hurled her friend's counterpart into the ground - where she disappeared into black smoke.
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~Fluttershy~
Now that her big mean counterpart was out of the way, Fluttershy hurried as fast as her wings could take her to Pinkie's side. The party-pony was trying (admittedly unsuccessfully) to make her counterpart laugh with a fake mustache and glasses. The opposite Pinkie was making a weird face in an attempt to do the same.
"Hey, you big meanie!" Fluttershy called - trying her best to sound scary. The alternate Pinkie turned her oddly shaped head and looked at her. Unlike what most Ponies thought of her, the true Pinkie was able to hyper-focus and keep her attention on a single target, a trait which her shadow-self seemed to share. This made her vulnerable to Fluttershy's stare - a fact which the true Pinkie took advantage of. While her counterpart was distracted, the party-pony loaded her party cannon and fired another blast of confetti. This one took her right in the back - making her disappear into... multicolored balloons?
Made about as much sense as anything else that happened today.
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~Pinkie Pie~
As soon as her double disappeared, Pinkie turned her head to the last of the shadow ponies - Twilight's. So far, she had been playing around with the princess, but she now stood over her friend, horn glowing. With her trademark pronking gait - Pinkie made her way to the shadow-pony's side and offered her most winning grin.
"Hey, Twilight-whose-not-really-Twilight, have you ever been to a real party?" The alternate Twilight looked at her in a funny way. "I don't think you have, cause the other me looked really boring! She didn't even look like she'd ever had a cherrychanga. Say, have you ever had a cherrychanga? Cherrychanga. Great name, huh? Oh, but maybe I should call it a chimicherry. Ooh, that's good too! Which do you think sounds better? Cherrychanga or chimicherry? Or what if I combine them? Chimicherrychanga! What sounds the funniest? I like funny words! Chimicherrychanga, cherrychanga, chimicherry!"
The other Twilight put her hooves to her ears and screamed.
Behind her, the true Twilight rose up with Applejack's help and fired a magic blast that disintegrated her counterpart. Now with all their opposites beaten, they were free to help their other friends.
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"Understand this, my friends..." Mirror-Sombra said, annunciating the last word with something like disgust. "-If you deny me, then the path to a future without fear will be gone forever. The things I have seen... you would go mad too if you saw them."
"I know all too well what such things hold, Sombra." Said Amore. "I have the gift of sight - and I can see what lies in another's heart." She pointed her hoof directly at him. "What lies in your heart is fear as well. You fear losing Celestia forever. And you fear... something else."
Mirror-Sombra nodded. "I am well aware of your sight, Princess Amore. You have visions of the future as well... just as my mother did long ago."
That got everypony's attention. Amore in particular blinked at that statement, then squinted.
"What do you mean?" She demanded.
"You do not truly think my path and his are one and the same, do you?" Mirror-Sombra asked. He did not wait for an answer. "Like him, I was born Umbrum, but I never succumbed to it. All thanks to you - or rather, the other you - was my mother once." He looked down, as if saddened by that statement. "She adopted me - and told me exactly what I was - but that did not change the way she felt. She loved me as her own son - even though I was different. Even when I was afraid I was a monster. Thanks to her - I was able to overcome that fear. Yet, I had to become a monster in order to see the truth; this world and ours - they are like me and him. They are defined by our choices. And so, I make the only real choice - by bringing our worlds together, I can create something better. I can ensure that such visions never come to pass."
He paused, then raised his hooves in a wide gesture.
"Don't you see? This is the only way to true harmony!"
"You're wrong!" Came another voice. Everypony turned and beheld Twilight and her friends galloping through the entrance. "True harmony doesn't come from forcing your will on others!" She declared. "True harmony comes from friendship!"
With that, the six element-bearers started to glow brightly. Their manes expanded, as did their Cutie-Marks. All present could not help but stop and stare. Fleetingly, Sombra realized what they were invoking must be Rainbow Power.
"No," Mirror-Sombra said quietly. In a moment, confusion turned to rage. "How could you have defeated your shadow selves?! How is it possible!?"
"Anything is possible when we work together." Twilight said. She turned to her friends. "Ready girls?"
"Ready!" The other element bearers cried as one.
With that, Twilight fired off the first beam - which struck the mirror being head on. Like before, when the Crystal Heart had vanquished him - cracks started to appear in his coat. A second beam followed it - followed by a third until all the elements were firing simultaneously. The rainbow blast enveloped the mirror-being, but to the true Sombra's surprise, he remained unharmed.
"What's happening?" He wondered aloud. His mirror self then started to exhale black smoke as the blast continued.
"Mirror-Sombra's evil heart is being cleansed." Amore replied, trotting up beside him. She looked at him grimly. "Be on your guard. The Umbrum essence is manifesting."
True to her words, the Rainbow Power drew out the familiar smokey substance - shaped vaguely like a Unicorn, but far larger and much more warped - and radiating a terrible dark magic. Gradually, the form shifted and turned into something not unlike Sombra's shadow form - green and red eyes glowing with malevolence. Behind it, the mirror-Sombra fell away, his coat and mane returned to its original color. Being stripped of the shadow power had made him too weak to stand - and it made his counterpart too weary to run or assist. Sombra's magical reserves had been drained from the fight before, and so it was all he could do to watch and hope.
"Now's our chance!" Amore cried. "Tia! Luna! Assist me!"
With that, Amore and the royal sisters stood up in a line - their horns aglow. The air around them crackled with energy as they let loose their full power. Without need to worry about harming Sombra or his counterpart any longer, they could now unleash everything. Once they had their strength gathered, they fired in unison. The blast ripped through the Umbrum essence, doing visible damage.
The shadow cried out in agony as the magic flashed through it. Yet, for all the power the princesses had, the Umbrum remained alive. With that, it expanded rapidly - shadowy tendrils flailing about and spearing everything in reach. The royal sisters scattered before the attacks - using their wings to take flight, each performed a series of midair spins.
Amore however was not so agile - a given that she was a unicorn, rather than an Alicorn. Instead she raised a protective barrier around herself. As she did so, another tendril shot forth - burying itself in the rubble beneath her. Before she could raise her shield again, a second tendril buried itself in her side. To Sombra's horror, before he could act, the tendril expanded - nearly tearing her apart from the inside. Suddenly, he found his strength again and fired a beam of his own - severing the tendril. Amore dropped to the ground, bleeding from a score of wounds.
Above, the mass of shadows quivered.
"Fools!" The shadow screeched. Its voice no longer hindered by a mortal form, it was as loud and piercing as a windigo's wail. "You think to destroy us!? There is nothing, no power on Equestria that can vanquish us so long as there are bodies to inhabit!" The shadow directed its fiery gaze upon the true Sombra. "You will all become part of us - starting with the traitor!"
At that last word, the shadow-being rushed at him with frightening speed - and Sombra's eyes widened in horror, but unable to bring himself to move. He had escaped the Umbrum's corruption - only to have that freedom taken away from him? Was this truly his destiny after all? Was it truly...?
"NO!"
At the last second, moments before the shadow could take him, Amore leaped in the way - putting her body in between him and the Umbrum. The shadow enveloped her - the tendrils reaching into her nose, her muzzle, seeping into every orifice and turning her bright pink coat into a sickly shade of grey, black and green. Yet, halfway through - the corruption was halted as streamers of multicolored magic took hold of her as well. The element bearers had turned their Rainbow Power on Amore. Now, they were attempting to draw the Umbrum from the princess.
"No," she murmured. "Do not release it." Her voice had taken on the echoing quality of the Umbrum, but it was still undeniably her own. Perhaps some part of her was still resisting it. "Let me die."
She turned her gaze to him, her eyes flashing between their natural shade of amber and unnatural green. There was warmth and compassion - mixed with hatred and cruelty in each color. She opened her mouth, but no words came out. Only a hacking cough - and she jerked her head to the side - clutching either side of it with her hooves. She stood up to her hind legs - jerking and rearing about frantically, as if her very body turned against her.
The element-bearers ceased their attack and allowed themselves to return to normal form. Grief and pain were on each of their faces as they watched Amore's life seep away.
"Sombra," she muttered. "...The Umbrum will perish with me. They will... never return."
At this, a great cry escaped from her throat.
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Outside the mountain - the shadow ponies that remained began to shriek and writhe on the ground. They died within minutes. Those that had been possessed were released almost immediately - confused, but alive and well. Shining Armor and his troops looked up - astonished, as the dark clouds above them began to part, allowing a bit of sunlight to break through.
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Tears filled Sombra's eyes as he watched Amore collapse. Her body was already starting to fade. Behind him, the element bearers looked on, powerless.
"Amore, no." Sombra pleaded as he leaned down - gently putting a hoof on her shoulder. "I did not ask for this. I did not want this."
Amore smiled.
"This world was not meant for me.... but there are others." She paused and coughed. When it passed, she reached up with a hoof and touched his face. "...And I will find my place among them, just as you have found yours."
As she spoke, the hoof began to disappear as well.
"Walk the path that is meant for you without fear - for you are not alone... not anymore."
With that, her body faded from sight - disappearing in a bright flash. As she did so, a final echo resounded through the chamber.
"Farewell, my friend. May we meet again."
Sombra buried his face in his hooves and wept - and he let the tears fell freely.