Blood Steward of Kirtonos

The Blood Steward of Kirtonos was a level 61 elite succubus found in the Reliquary in Scholomance.

She was added in a patch as an additional source of Blood of Innocents. But to get to her, you need to clear nearly the entire Reliquary. It's was optional to kill her as Jandice Barov and Doctor Theolen Krastinov will also drop the Blood.

Miscellaneous Fun
She can be enslaved by a warlock.

She guards a book lying on a table titled "The Scourge of Lordaeron" which tells of Kel'Thuzad releasing the plague of undeath on the City of Lordaeron and of Prince Arthas' failed attempts to save the city. As he tracks the plague to Northrend, Arthas comes to wield the cursed sword, Frostmourne, but yields his soul as well. The Prince ultimately becomes one of the Lich King's greatest death knights.