This is called a Ponysona, an OC is any character that is original.
As for names...
Frenzy, Little Bite, Feeding Frenzy, Lady Vain, or vain lady
For some reason I'm liking frenzy...
NightFrenzy
ShadowFrenzy
SecretBite
FeedingFlight
BeautyBlood
Cutie mark,....a heart with two holes in it....a coffin....a mirror