Your Worst Enemy Could Always Be Yourself
"Why, why can’t they accept me? They accept and crazy ol' Pinkie, they accept that worry wart Twilight, and even that crossed-eyed and clumsy mailmare, Derpy Hooves, who they even gave a pretty cool nick name even though she always puts the mail in the wrong box! They welcome every PONY with open hooves, they welcome every zebra, every griffon, every cow, every mule, even Minotaurs, why not a draconequus? Why does nopony except Pinkie Pie and Fluttershy accept me, Pinkie Pie only likes me for the chocolate milk and cotton candy anyway. Why am I the one that the little fillies are told to stay away from? They know I'm not evil or cruel anymore, but they still treat me like a monster!" muttered Discord as his sadness slowly turned to jealousy and rage as he stared at the frolicking ponies outside his chaos-filled room in Canterlot Castle (1), resentment grew in his heart.
"Look at them so HAPPY! Is it worth it... all this sadness for two mortal friends, they aren't going to last forever, their lives will just be a second compared to mine, maybe I should try to become friends with little miss egghead like Fluttershy suggested, wow, I'm so depressed I actually considered becoming friends with Princess Egghead! Why indulge in something you know you can never replace, where's the point in THAT, it’s not just nonsensical, it's downright stupid!" He said as he started tapping his fingers on the windowsill, wondering what it would have been like if he hadn't betrayed her, the first living thing that had actually cared for him, even more than his own mother, or his only two friends, Fluttershy and Pinkie Pie, now she was gone, and he had no idea where. He suddenly felt a strong powerful, yet dark presence behind him.
"You're right as always, Discord, those ponies not worth it, you don't deserve this cruel treatment, join me, you get Equestria, power, and your fun and I just get sweet sweet revenge on the one who betrayed me!" said a voice like a silky purr with a gentle, almost innocent sounding tone. The kind that Discord knew not to trust, or at least he would know, if he wasn't in such a state of distress. He had used that same convincing tone many times to corrupt ponies, to bend them to his will, it was the kind of voice people that make ads with sound could only dream their voice actor or actress could have.
"Pray-tell, who -or what- are you?" Discord asked tentatively, wondering who, or more importantly what, this strange intruder was. Looking closely at the creature he noticed that it appeared to be a blob of dark bluish-smoke with a lighter, translucent edge, this being never seemed to stop moving in waves, like Celestia's mane. It looked familiar, maybe like a certain alicorn princess's mane, or at least, their mane while they were evil.
"Oh, the answer will come in due time," the voice said sweetly, quickly flashing with each word and speaking in a 'let's just get to the point' voice, "for now, just think of me as... a friend. A friend that, with just a little help from you, will let you rule Equestria with more power than you could ever dream of! All you need to do is agree to let me help you." The 'thing' had started to swirl around Discord, like he had around Pinkie Pie while graying out (2) her.
"I get to rule Equestria in MY own way? With the chocolate rain and everything else I love?" said Discord as he stood up and started pacing, considering the option, wondering how this could go wrong, or how this could go right. Oblivious to the lie the voice was feeding him, similar to how he fed lies to the oh so powerful Elements of Harmony, he continued believing.
"Why, of course, I said YOU would rule it didn't I?" The voice said slyly, realizing this might be way easier than it had anticipated. If it had a mouth it would have had a vicious grin.
"Power... enough to defeat the Elements of Harmony?" Discord said with a slight purr, warming up to the option, realizing that this would be the only bump in the road he might encounter with this things plan. He did not realize how little detail he had been given.
"Possibly enough to DESTROY them!" the voice said enthusiastically, knowing it had Discord right where it wanted him and realizing he did not have to do much work to break the spirit and get control of his mind...
Meanwhile,
(1) Chaos-filled to say, he had warped reality to make it to be as big as Ponyville, in fact, it WAS Ponyville, just his chaos-filled version. Also, his bed was alive and running around, trampling over the fake ponies Discord had in there, Discord is really messed up. Also, in his fake Ponyville, Fluttershy and Pinkie Pie were enjoying the chaos while the other elements of harmony were the main targets of his bed.
(2) Graying somepony out is known as 'Discording' by the ponies, it is actually a common draconequus trick (Discord isn't the only draconequus in this universe) Discord does not take offense from ponies using the term 'Discording' or 'Discorded' though.