So backstory is that Sunset Shimmer’s demon form is an actual shapeshifting demon pony race which comes from Tartarus(because they were DUN DUN DUUUN banished there). Sunset was slowly changed into one by a certain individual. I’ll give you an imaginary cookie if you guess who it is.  
HINT: It’s not Big Mac. Though you probably would have guessed that anyway.
 
The hair is lineless because I was lazy. Also, I wanted it to look like fire, but I kind of failed.
 
Neon bluish-green and burgundy go surprisingly well together.  
I’ll draw different ranks of demon ponies soonish.  
MLP (c) Hasbro.  
Made in SAI.