Edit: Yes I realize that one hand has 4 fingers and the other has 5
That was just a bit of an oversight on my end
This is a redesign of Princess Ataxia/Imposter Rosequartz Lustre
Ataxia
Rosequartz Lustre [the pony she's imposing as], Lucy, Mecha [by Tinker]
Family: Chrysalis [birth mom], Exo [birth father], Entropy [half brother], Flurry Heart ["sister"], Cadence ["mother"], Shining Armour ["father"]
Special Talents: Deception, Chemistry/Mechanics/Physics and mimicry
Ataxia was born out of a need for vengeance and hatred. Her mother Chrysalis has been planning a more advanced method of revenge against the ponies of Equestria.
While a few others of her hive are strategically placed around Equestria, Ataxia is her most prized weapon as she's been trained to impersonate a deceased member of the Royal family.
Chrysalis used a young Ataxia to lure Cadence and Shining Armour's youngest child Rosequartz Lustre out of her home and personally ended her life to replace her with one of her own brood.
For 20 years Ataxia has been impersonating Rosie and keeping an eye on the Royal family. She was instructed to cause instability within their ranks by finding the weakest link. She chose her "cousin" Stellar Rays and merely backed up the hateful hearsay and planted a fear of inadequacy when he came to her for support.
For her part, Ataxia is a jaded creature. She feigns superiority to keep ponies away but that doesn't always work. She unintentionally caught the eye of Tinker Sundance daughter of Rainbow Dash as they share a love for technology and science. Tinker is the only person Ataxia actually likes and even she isn't out of her range of fire.