WARNING. MAJOR SPOILERS FOR GEHENNA BOOK.
Ok, does everyone know about the Slenderman mythos? How he's a white man with a black suit and red necktie and has no face/facial features?
He's also described as having an alluring presence, making people want to walk to him. He can make a person's body move without the person's consent, and often messes with their memories of the events including him, as if engraving himself on those people's very souls. Through this, he has a "habit" of making "proxies" through which they do his unknowable work. These proxies subconciously do things for the will of Slenderman...WHATEVER its will is.
He also warps. Alot. Usually he does so when he's outside of your flashlight range. Or in other words, though the darkness outside of the light. There's also how each time he's seen, he erodes some of that person's will and/or their mind. He also creates black tentacles out of his body when he wants to capture someone or something.
WARNING MAJOR GEHENNA SPOILERS WARNING
I was reading through the Gehenna book, and here's what I've came upon when I saw Lasombra's entry.
"This Antedeluvian could possibly be the source of humanity's fear of the dark. Few things seem more horrendous than control over darkness and shadow.
...When the clan rebelled and turned on its sire on Castillo d'Ombro (Castle of Shadows/Darkness) during the Anarch Revolt, Lasombra allowed its childe Gratiano to diablarize it. As it's soul was released, it did not enter Gratiano, but rather entered the Abyss, with which Lasombra has potent ties. Through centuries of being incorporeal, the ancient worked its designs through LESSER PROXIES who sometimes would venture too deep into the Abyss and come under its sway. UNBEKNOWNST TO THEM, these proxies would work toward restoring the Antedeluvian when the time was right..."
In the Nightshade part, it states "Lasombra is an ominous shadow, it's presence more felt than seen."
Montiano, Lasombra's first and loyal childe states that his memories were tampered with on the day of his supposed "diablerie".
And then there's looking through the powers of Dominate and Obteneration. The best ones?
Dominate 4: Conditioning. Over time it can erode a person's personality and sanity, making them slaves to the user's will alone.
Dominate 5: Possession. This requires a person to have their willpower completely spent. They can then go into that body, manipulating it.
Dominate 6: Autonomic Mastery and Rationalize. The former allows for controlling a person's movement and the latter makes a person believe any action through which the target was commanded by Dominate to believe it was completely of their own will.
Dominate 7: Strings of the Marionette and Tyrant's Gaze. Former allows for controlling while in Torpor and latter has Attributes falling by a certain degree by establishing a look at each other.
Dominate 8: Carry the Master's Voice and Far Mastery. Former: Allows for ghouls to use Dominate 1-3 on people
Latter: use Dominate on anyone as long as you know where they are.
Dominate 9: Best Intentions. Self Explanitory.
Dominate 10: Puppet Master. Turns people into a replica of you in mindset. Look at "Slenderman Woods Ending" for a better idea.
As for Obteneration...
Obteneration 3: Arms of the Abyss. Create Black tentacles from yourself or shadows.
Obteneration 4: Black Metamorphasis. Grow nightmarish armor and sport black tentacles from body.
Obteneration 6: Shadowstep and The Darkness Within. Former: Teleport from shadow to shadow
Latter: drain a person of blood via shadows (Again, Slenderman Woods Ending).
Obteneration 8: Dark Hunter. SELF EXPLANITORY.
Obteneration 10: Banishment. Gotta make things disappear somehow.
TL;DR - LASOMBRA IS SLENDERMAN.
DUN DUN DUUUUUUUUUUUUUUUUUUN