Bad Powers, Good People: Though noted for the PC character already, The Final Nights introduces plenty of creepier powers.
This is both a blessing and a curse, as they get so absorbed into what they specialize in that they don't track things outside of it.
Badass Bookworm: The Assamite Visier, who are just as capable fighters as the main clan, but are more scholarly focused.
Aura Vision: The Auspex Discipline, used by the Salubri, Assamite Visiers, and Osebo.
The Baali's weakness is that their Humanity is capped at Humanity 7, but there's nothing keeping a player from trying to keep it up anyhow.
Always Chaotic Evil: Played with and can be subverted.
The Clans/Bloodlines introduced include Osebo, Ishtarri, Salubri, Assamite Visier, Samedi, Baali and Warrior Setite. Within the Final Nights Mod, it's possible for the Player Character to be one of the new Clans/Bloodlines added in.
Teleport Spam: As a Lasombra, he has the ability to teleport short distances.
No Name Given: He's only ever referred to as "the Lasombra".
Human Sacrifice: Presumably performed these underneath the library, and nearly killed Beckett's associate as part of a ritual before the player intervenes.
"Get Back Here!" Boss: Indulges in Teleport Spam throughout the fight, peppering you with SMG fire before retreating when you get close.
Snooping on his computer during Beckett's quest will reveal that he was trying to recruit the Slasher to the Sabbat, but escaped when you intervened.
Early-Bird Cameo: He's first seen teleporting away when you're looking for the Southland Slasher.
Beard of Evil: He sports a wicked looking goatee and is affiliated with the Sabbat.
Badass in a Nice Suit: In contrast to lesser Sabbat minions, the Lasombra is dressed quite nicely.
All There in the Manual: He could be a member of Angellis Ater or Azaneali, considering the area you fight him.
While not part of the original game, he and his quest are included in some fan mods. A Lasombra vampire in service to the Sabbat, performing rituals underneath the Downtown Library.