At some point after the events of the show, Equestria is attacked by seven demons, each named after the sin they represent: Lust, Gluttony, Sloth, Greed, Envy, Pride, and Wrath.
The mane six find themselves unable to defeat the seven in their first encounter, but afterwords are greeted by one of the seven, Envy, who is willing to parley with them. Envy has no love for his siblings, and agrees to help the mane six defeat them. He reveals that while they are together they are too much for the mane six to handle... but separate they would be easy to pick off one by one. Envy sets up his siblings, getting them to split up. Each one is eventually defeated, but curse the pony that played the biggest part in defeating them.
Twilight is cursed by the magical savant Sloth, Pinkie Pie by the uncaring Gluttony, Applejack by the cruel and twisted Pride, Rainbow Dash by the enchantress Lust, Rarity by the clever Greed, and Fluttershy by the brutish beast Wrath. These curses twisted them either ment