Prankie Shellshocked
Prankie Pie lives in Ponyville, along with Derpy Hooves and her human artist, Zander. As her name would suggest, she has a love for pranks, which she pulls on her friends and acquaintances as often as she can, even going as far as pranking Princess Celestia in her sleep. She has been seen with different accessories, but now only wears a single necklace, which rarely leaves her person.
The inhabitants do seem aware of the different tumblr ponyverses, as evidenced by Prankie identifying herself as 'the more tricksy version of her Ponynet friend, Pinkie Pie', but as of yet, no interaction has been seen between her universe and the others, short of normal ordinary questions which she answers with the help of Zander.
Thus far, there has been no explanation either to why she has such a love for pranks, how a human came to be in Equestria in the first place, or how they manage to pay the rent, although Zander has hinted that he supplies it for them.
Thus far, there has been appearances by Prankie, Derpy, Zander, Rarity, Fluttershy, and Princess Celestia, with mentions of both Rainbow Dash and Applejack. There is a confirmed relationship between the two, but the seriousness has not yet been explained other than 'dating'.
Prankie has been seen to possess at least some of Pinkie's supernatural world-bending powers (she changed Zander's shirt graphic numerous times during an update for the sake of a joke, as an example), but nothing extremely notable has happened yet.
The blog may be found at Ask Prankie Pie, while the artist's mod blog may be found here (Mildly nsfw).