Prologue: The Beginning Of Terror
One calm sunny day, a dreadful thing took place in a deep, dark cave in Equestria: A cave wherein nopony can enter and exit. In this cave is where Flamina, the former flaming princess of Equestria that caused terror and chaos worse than Discord, is arrested. She is behind lightning bars coated with anti-magic, so that she can't use magic to escape. To make it less confusing, just imagine Flamina as the fire version of Nightmare Moon.
One time, the King of Darkness, Pitch (more like King Sombra but darker and fiercer), went to the cave. Then, the foundations shook, the rocks feel down, and the lightning bars splitted into pieces, with a zap of a mist from his horn.
"How'd you do that?" said Flamina.
"It sayd you can't use magic from the inside, not from the outside" said Pitch, "Well, it is as promised" said Pitch "I set You free, you hand me over Equestria."
"Very well, then" said Flamina "but first, and foremost, we need to take the throne, and I know just how to do it"
"Whatever it is, do it" said Pitch, in a deep, dark, voice.
"See that?" said Flamina, pointing to a large tower on the Northern West side of Equestria "That's where the sacred 7 keys are stored. Each key open a box full of terror and chaos. Once we opened those 7 boxes, Equestria will be ripped like paper, and You can take the 7 pieces of Equestria."
"Very nice plan." said Pitch, "We should take it and then..."
"But, wait!" shouted Flamina, "The tower is guarded by elemental magic, placed by that Celestia. We can do a counterpart of that magic, but with us alone, we can't succeed. It might be even the cause of our extinction."
"So, what are we to do?"
"The only way to succeed is to do a counterpart with the Elements of Harmony, and I know where to start."