Stygian (Mirror-Universe)

Stygian was a unicorn stallion from somewhere in Equestria. He was a member of the Pillars of Equestria of his world before his fall into darkness.

Fall to darkness
Stygian never lived an easy life. Assuming his life was similar to that of the Stygian of the "main" universe, he was often taken advantage of by his peers who refused to show him respect. At some point he met and befriended the Pillars of Equestria, though they only made his life harder. He truly did care for Rockhoof however, and was deeply saddened by his death. Stygian's depression and misery would fester for years to come until he was truly cruel and malicious.

Stygian sought to kidnap the royal sisters of his world. He was, however, stopped by Starswirl the Bearded who valiantly fought to protect the girls. The Pillars attempted to seal themselves and Stygian away in limbo, but Princess Eris intervened and Stygian was able to kill Starswirl. The other Pillars escaped with the Princesses, whom Stygian became even more determined to corrupt after studying Starswirls' research. However, he was unable to locate them, and thus turned to searching other worlds through the use of magic mirrors.

Interactions with Equestria
When of Equestria managed to open a portal to his world, Stygian didn't hesitate to kidnap her in a attempt to forcefully break her mind. She was soon saved by her sister and Starswirl, but the experience would continue to haunt her. Some time later, his monster minions broke into the Castle of Two Sisters to kidnap the two princesses. Their Starswirl heroically defended the girls but he was ultimately defeated. The girls themselves put up a respectable fight but the monsters were to much for them and they were forcefully dragged into Stygian's world.

Starswirl survived the encounter, albeit barely, and was joined by his world's Stygian, Rockhoof, Somnambula, Mistmane, Flash Magnus, and Mage Meadowbrook. They opened a portal to Stygian's world, and after splitting up engaged many of Stygian's minions. Stygian later attacked Flash before confronting Starswirl, whom he recognized as a counterpart of his old friend-turned-adversary. He attempted to destroy Starswirl, but was distracted when his own counterpart sent up a flare announcing that he had found and Luna. Arriving quickly at the site where his minions were outfitting the unconscious princesses in armor, he found Rockhoof and the other Stygian and explained his plans for the girls.

Though saddened at the memory of his own Rockhoof's fate, Stygian was puzzled by the presence of his own counterpart, whom he failed to recognize. The other Pillars of Equestria then arrived, and a battle ensued, with the other Stygian rushing to save the princesses. The pair confronted each other, unleashing their magic against each other; surprisingly, Stygian found his powers checked and was thrown backwards. He ordered an ogre to grab the princesses, but was then shocked when it obeyed the other Stygian's command to toss them to Starswirl. Utterly flummoxed, Stygian demanded to know the name of his foe and vowed to find him, only to learn that he had been fighting another version of himself.

Downfall
Despite his defeat, Stygian became more determined than ever to corrupt a Celestia and Luna to join him in his dark conquests. As such, he approached Eris, seeking her help in locating them, but the goddess of luck refused to cooperate. Stygian responded by taking her prisoner, and spent the next few centuries drawing on her chaos magic as he continued his search. Eventually he succeeded in capturing and keeping a pair of princesses, whom he corrupted into Daybreaker and Nightmare Moon. However, as he trained the pair for their dark duties, Nightmare Moon failed to live up to his expectations.

Eventually, Nightmare Moon tired of her master's cruelty and attacked him, pleading with Daybreaker to join her in doing so. However, Daybreaker was more loyal to the Pony of Shadows, and struck down her sister for good. Wanting to insure that Daybreaker would not turn against him, Stygian approached Eris for help. She created a collar that limited Daybreaker's powers, but designed it so that she would be in control. Eris then had Daybreaker free her, and they attacked the Pony of Shadows together. With Stygian defeated, Eris was then free to step into his place as ruler of their world. She would later disguise herself as Stygian in order to lure Equestria's Luna back to her world and steal her powers.

Return
Despite his implied demise, Stygian-or else an identical alternate universe version-would later invade Equestria, forcing the Mane Six,, the Pillars of Old Equestria, and the Young Six to join forces to stop him. The task proved difficult, as Stygian would use his power to bring allies from various realities to aid him. These included Nightmares, unreformed Changelings under Thorax, Shadowbolts commanded by the Tantabus, several Umbrum, Well-to-Do and Princess Eris, and mummies led by King Anubis. As such, the heroes divided into teams, each representing a different one of the Elements of Harmony and coordinated by Starlight. Ultimately, his minions were defeated and Stygian was freed from the Darkness, with his former enemies welcoming him to their world.

Personality
In his youth, Stygian was kind, polite, courteous but horribly insecure. He suffered from self-esteem problems which eventually festered into him turning to the dark side.

As the Pony of Shadows, Stygian was incredibly wicked, cruel and uncaring. He killed Starswirl the Bearded in cold-blood after he watched his friends die one-by-one. He wasn't completely evil however as he still cared for Rockhoof, but this was only a single good spot in a truly vile personality. He kidnapped Princess Celestia and Luna in order to brainwash them into becoming his slaves of evil, though he was ultimately stopped by Starswirl. Stygian was serious and brooding, but also emotional and passionate. He was incredibly vocal about his plans to erase reality and bragged about how the princesses contained infinite power, but remained somber when he no longer had company.

Stygian was deeply unnerved by the realization that Stygian was himself from another world, and marveled that he could have changed so much as to not recognize himself.

Appearances

 * (possibly was the voice that spoke to Luna, but it's unclear)
 * Legends of Magic Annual 2018
 * Nightmare Knights issue 1 (as a disguise for Eris)
 * Nightmare Knights issue 4 (flashbacks)
 * My Little Pony: Magic Princess (as both Mirror-Universe Stygian and Pony of Shadows)