#classical unicorn

Stygian’s distant descendant, the last living branch in his family tree

Lives alone in his family’s castle after they retired to the town of Somnambula

Temporary antagonist to the mane 6 that stems from a fear of the Pony of Shadows returning to plague Equestria

Believed he was descended from a monster and desperately tried to erase any mention of the Pony of Shadows from written history

Was talked down from his history erasing spree by Twilight and ends up traveling around Equestria to find more info on the Pony of Shadows, without trying to erase the knowledge this time, and prevent it from returning

The symbol on the front of Shadow Lock’s cloak is his family crest that dates back to Stygian's time period.

There’s a glamor woven into Shadow Lock’s cloak that enshrouds its wearer’s face.

Shadow Lock’s special talent is the concealment and binding of dark magic. He can effectively bind malevolent “spirits” into vessels where they’re unable to cause harm. This can also be reversed as an unbinding spell. ("spirits" in this context are more like a culmination of lingering, concentrated dark magic that takes on a will of its own)

His family castle used to be quite “haunted”. It’s quieter nowadays, but he does have a large collection of miscellaneous items that most ponies would consider “cursed…”

Always carries a healthy stack of books on his person to read and use as a weapon. His spells can pull fictional characters and monsters from stories to fight for him

Created a spell that can trap a creature into experiencing a historical event on loop by using a small amount of written text. The spell can be broken by doing something significant enough that did not occur during the looped event in history.

Shadow Lock and Stygian are extremely hesitant to meet each other at first in present time. The mane 6 and Harmony step in as mediator eventually to help them work out their issues so they can reconnect as family

Much later in the story, Shadow Lock invites Stygian to live in his castle once their family relationship is repaired, the two becoming inseparable

His original design from the comics: