Stygian

Stygian is an Equestrian Earth pony who used to be a friend to Starswirl the Bearded who helped guide them to a path of spreading the power of him and his Pillar friends across Equestria. However, wanting the power all to himself, he was cast of his duties by Starswirl, as he changed into the infamous Pony of Shadows, and cast all 6 Pillars to limbo, and it is where they remained to this very day, unaware that during the time, Starswirl left hope in the form of the Tree of Harmony, and by extension, the Elements of Harmony, to offer a chance of stopping the Pony of Shadows once and for all.

(TBC...)

History
Coming soon...

Role in the series
Stygian is revealed to have lived during the Equestrian Great Fear Wars when Pitch Black was still reigning supreme. After Pitch's rule left his family to vanish, Stygian was left on his own, leaving Starswirl as the only family he had left, and by the time he got greedy for power as the result of his loss, and with Starswirl casting him out and thus making him feel abandoned once more, Stygian got embittered and turned to the dark ways of Pitch himself for answers. Thus, he turned him into a Taraxippus, the boogeyman of Equestria, and later on the new Pony of Shadows, as this allowed him to cast Starswirl and his friends in the Pillars into limbo, halting their aging in the process, and allowing Stygian himself to fabricate lies of their disappearance to discourage the hope they had, and after hearing that, after Pitch killed the Tree of Harmony of ancient past to keep Celestia and her family from defeating him with the Elements of Harmony (As he knew that a few side-effects would've gone with the disappearance of the tree such as Discord's plunder weeds and didn't need to replace the Elements themselves), Starswirl planted another to act as a final stroke of hope. Thus, after Stygian was cured of his corruptive influence, the Taraxippus race swore revenge by not just going after others, but Stygian's long-lost sister Halo Epiphany, who was trapped in limbo like Starswirl and stopped the previous Pony of Shadows from taking Celestia and Luna with the same unknown fears Pitch used against them, by sacrificing her soul to save them and earning her a fancy mark (A cutie mark that covers the entire body as a result of the highest display of talent), and joining the Guardians of Harmony, while not knowing that his brother Stygian is still alive, and as she came back from limbo eons after her imprisonment as limbo is out of sync with the UUniverses' timescale and can cause temporal distortions of many kinds without the proper spell, and after hearing right away after the events of Shadow Play that his brother was still alive, she swore to find him.

(TBC...)