A few things to mention...

-This is an alternate world following the events of season 3. while season four is now on the air and I may use an element or two from it (if it helps this story) this will be my own head-cannon/continuity of the series, thus any comments berating me for not following canon of season four will be removed.

-To be honest... I making alot of this up as I'm going along so suggestions for advancing the plot are welcome. I know its a bad Idea to make stuff up, I at least have a skeleton of what I have in mind, I just need to flesh it out.

Taking a quote from Legend of Korra "One cannot survive without the other" and from my own beliefs, "even the purest person has a dark side."
In Return of Harmony we see Discord bring out the opposites of our heroine six, and honestly I wasn't impressed. but it got me thinking,
"We know about the elements of Harmony... but what about a set of dark elements?"
Now being the direct opposites of the Harmony elements is too cliche and predictable at best. So another quote I live by chimed in (Thank you Tomorrow Never Dies) "The key to a great story isn't who, or what, or where... but WHY?"
And thus came the Elements of Corruption... and that's all I'm going to say on the matter. If you want more just wait for the next page.