Nightmare Rarity comes from the official comics. You can find these comics on iTunes or on Yay Ponies.

------------------------------I figured that Nightmare Rarity from the official comics needs a proper vector.Her name is well-deserved - this is easily the most insane manestyle ever put on a canon pony. These little stars (or grain, as I call it) were a bit troublesome too. I decided to upload them as well, so you won't have to bother with them if you were to make some Nightmarity yourself; you can find them linked below.---------------This vector was created from scratch in Inkscape, using only a mouse and no sketches of any kind.Featured in EqD's Drawfriend #798: www.equestriadaily.com/2013/05… ---------------