Everypony knows the Royal Pony Sisters. Nopony knows the Undying Alicorn Brothers. That's how they prefer it as it's one of the main reasons that they've lived so long, and they have been alive for a very, very long time... since long before the Sisters, the brothers were causing floods, spreading plagues, summoning blizzards, and generally being unrepentant mules. No offense.
"None taken."
In any case there are ancient stories and legends centered around them, that fortunately nopony but the most scholarly and antisocial ponies read up on. But those who do know the legends know this... that in the time when Alicorns were considered deities, the Brothers were considered to be the Gods of Evil, darkness, and everything wrong within the hearts of ponies. And it's a good thing that nopony thinks they exist, because if they did they might be laughing at how hard the brothers are failing right now.
They're failing. Losing. Getting their rumps kicked. Celestia's new happy squad of merry Element Bearers is running roughshod over every big bad they can get their hooves on, and for all their strength and power, they can't stop it without revealing themselves to Celestia... and promptly getting their flanks handed to them on a silver platter. With their biggest baddies out of commission, and Celestia's huggle-hardened Bearers of happiness and sunshine trampling over the last bastions of darkness and evil in the world, the Brothers have resorted to desperate means... Mainly they've picked a new pony out of the crowd to gift unbelievable dark powers to.
The new kid comes from a bad background, has very few social ties, and is currently at the bottom of life's barrel. Perfect. He's also something of a whining simpering doormat with all the spine of a dissected jellyfish. Like I said, "desperate". But what he does have in abundance is POTENTIAL... and since ancient laws and survival instincts bar them from directing his efforts personally, they've decided to leave his education up to the next most repulsive, twisted, sick, demented, and all-around psychopathic source of evil that they still have access to. You.
(I had this idea after seeing all the really sick and twisted Ask Pony Tumblrs. I wanted to do something like that, only thing is while I have some marginal skill with words, my drawing skills are less like skills, and more like underdeveloped kindergarten level doodles. So, drawing's out, but there's a lot of cool interactive fictions on this site that show that commentator participation can be loads of fun, so here's my attempt at a commentator driven/aided/participated in story!
Mainly it works like this. At a certain point in the story, and you'll know when, the new bad kid's going to get selected, and then you'll be able to put little ideas into his noggin. The point of the game is to encourage him to badness! And hence the Mature rating, while I don't know how far this is going to go I fully believe in two things, description, and letting evil nutcases be evil nutcases. I'm not saying that he's going to start off dissecting school-foals with a rusty spoon, but if you all push him that way, then you'd better be ready to watch him sharpen a spoon while poor little Applebloom shakes on the table.
Conversely, you can do the opposite, you can get the character to throw off the evil shackles placed upon him and embrace a new life, overcoming the temptations of darkness! ... Yeah, let's just bask in the fantasy that the internet community would go that route for a moment... Mmmm... ... Okay, now that that's done, back to the point. The point is that this is a story that is based around evil but will go how the crowd pushes it, so... Let's see if you've got what it takes to craft Equestria's next biggest villain... And what type he'll be)