Discord sat down. He sipped his tea casually. "Our son is being a very naughty boy."
Nightmare spat her tea out. "Don't call it that!"
Discord chuckled. "Oh, come now Nightmare, tell me you don't feel the least parental pride. We merged powers and out came this immensely powerful universe destroying menace. I may not agree with his methods or goals, but you have to admire his dedication. He set out to end the universe, and here he is destroying it one piece at a time."
Nightmare growled. "He's destroying the moon and stars!"
Discord smiled fondly. "Yes, he has the keys to the universe, and is wrecking everypony's toys. Still, he is a naughty child."
Rarity sipped from her cup. "Really, I don't mean to interrupt this truly horrifying display of pride, but I must insist on an explanation here. Why are you two apparently imprisoned inside the chest of the monster we just now drilled into?"
"Oh, is this that scene then? The villain explains how his plan went horribly wrong? How he created his own prison? My, doesn't that sound perfectly boring. How about we do something interesting instead, we go outside that door you kindly made, and send my son to his room. You can speculate on my motivations the whole time while I am doing it." Discord flashed a winning smile, his one fang somehow gathering the light in the room to flash impressively.
Sapphire glared at him. "As if we could trust you!"
Discord sipped his tea again. "You'd be a fool to trust me, but just because you can't trust me doesn't mean you don't need me. Come now, you tried the Elements and failed didn't you? Then you tried drilling through his armor to see if you could get past the barrier enchantments by force, correct?"
Rarity nodded. "Yes, that's it exactly. We'd be trying the elements on the hole left behind right now if I hadn't found the two of you here."
Discord nodded. "You're thinking about this all wrong. Let me venture a guess, Twilight Sparkle found out the armor absorbed magic?"
Rarity nodded hesitantly.
Discord smiled encouragingly. "So you came to the perfectly logical conclusion, remove the armor, and win the day? Yes, that would make sense wouldn't it? That is, it would, if you weren't dealing with a being of pure chaotic energy empowered by another of hate fueled magical potential. No my little ponies, logic will not help you here."
Rarity could not believe what she was hearing. "I refuse to believe this ruffian is invincible!"
Discord shook his finger. "I never said that. I said logic will not help you here. Logic has in fact fled the scene, probably off playing cards as we speak. What you need is right here."
Rarity looked at him nervously. "Give me one reason."
Discord laughed. "I'll give you several! I am chaotic my dear, what that monster out there is attempting will reduce the universe to pure uniformity, there is no more perfect order than nothingness! Perhaps that is not the most noble of reasons, but it's what you're getting. Also, while I have certainly delighted in turning your world upside down, I find live victims far more amusing than dead ones. Finally, while it may not seem important to you, it would not be boring!"
Rarity looked him in the eye, studying every twitch. "I believe you, it makes no sense, but I believe you. I am not certain if that makes me more insane than you at the moment."
Discord just smiled. "What fun is there in making sense? Nightmare, would you care to join us?"
Nightmare looked pensive. "Join the very ponies I was trying to kill, against a being trying to unmake everything with my power and yours combined? I supposed it's better than being banished to the moon again. Although I expect that's coming anyway."
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Everypony stared at the dark hole in Omega's chest. This... Was not what they had expected to happen.
What followed was easily the second most improbable thing to happen that day. From the hole popped four ponies. Well, two ponies, a draconequus, and a pony shaped spirit of malice. Discord flew up into the face of Omega, hands on his hips.
"Son, I am disappointed."
Omega looked down his nose. "You."
"Yes."
"You are irrelevant. I have your power."
"Do you?" Discord snapped his fingers, and an anvil fell from nowhere and smashed into Omega's head. Upon impact it turned into one million lightly fried eggs.
Omega glared, not hurt so much as surprised. "How? That doesn't-"
"-Make sense? Really now, does nopony get the concept of chaos?"
"Fine, if I cannot take your power, I will have hers." He pointed at Nightmare, and her dark flames began to flow towards him.
Nightmare screamed as her power was taken from her by force. She looked at Discord in pain. "I trusted you! Why was I so foalish?"
Discord leaned in, "Trust me again for one moment. Don't fight him, give him everything. Give him your pain, your anger, and all of your sorrow. Make him choke on it."
Nightmare stared for a moment, then her dark fire flared, and the stream of power headed towards the colossus became a torrent. His dark armor cracked under the strain of the energy pouring in.
At that moment third most improbable event occurred. Celestia and Luna teleported to the scene at that precise moment. To say they were shocked at the scene would have been an understatement. So instead, we will go with flabbergasted.
Discord snapped his fingers, and the armor plating turned to pudding.
Celestia opened her mouth. "What-"
Discord shook his head. "No time, you have exactly one shot at this, everypony gather and put every bit of energy you can into the elements.
Twilight looked at Dawn, who nodded, they began gathering energy. All of the bearers and elemental alicorns gathered into a group and poured their energy into their respective element of harmony. Celestia and Luna joined them, adding their own power to the blast. The rainbow that came from the combined powers held every color imaginable, and several beyond imagination. It struck the giant, and Omega exploded into pure energy.
All around them, the missing parts of the world and the sky were restored. The sky was awash in color. The moon hung in the sky, visible despite the sun shining high in the sky.
In the aftermath, an alicorn flew unsteadily where the figure of Nightmare had been. She had a dark mane full of sparks and a black coat. The dark fire that had covered her was gone. She looked confused. Discord patted her mane. "Well done."
Discord looked at Rainbow Dash. He nodded at the sunglasses on her head. "Mind if I borrow those?"
Rainbow looked at him as if he were mad, then remembered whom she was looking at. She shrugged, reached up with a hoof, and tossed them at Discord.
Discord placed them on his head. He posed casually. "Make it quick will you? I would at least like a better pose this time. It gets so tiresome spending eternity looking as if you just had a bucket of water splashed in your face."
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Celestia stared long and hard at the one entity she ever truly hated. She still was not certain what had happened. However, she had an obligation to her people to deal with threats to their lives and sanity. Nightmare and Discord were both. Yet she was hesitant. She had just witnessed the single most improbable event she ever expected to see. Nightmare and Discord had just worked together, to destroy a threat greater than either of them had ever represented.
"Princess."
Celestia looked at Twilight Sparkle.
"We shouldn't do it. Neither of them represent a threat we cannot overcome at this moment. I need to tell you about something before we make any decisions."
Celestia still had little idea how to process these series of events, but she trusted Twilight without question.
"Discord, Nightmare, you are hereby placed under arrest by the authority of the crown. You will be held unharmed until such time as a trial can be convened to decide your fate. Resistance will be met with immediate punishment. Do you both understand?"
Discord lowered the sunglasses. He nodded slowly and carefully.
Nightmare was still confused, she wanted to feel something, but she just felt empty. She realized she had no idea what it felt like to not be full of rage constantly. She nodded as well.
Celestia looked back at the mountain where her home should have been, the facade of her castle had apparently been eliminated in the explosion of magical energy just now. "Oh yes, would somepony mind getting my capital out of that snow globe?"
Discord snapped his fingers.