Whenever a power calls for spending blood, the blood pours out of a cut the vampire inflicts on herself (or from her mouth, tear ducts and other openings) and crawls through intervening space to the chosen area of effect. A vampire using Shroud of Night therefore disappears momentarily in a fine mist of blood, while Arms of the Abyss calls forth jets of blood that plunge into target shadows and animate them. These cuts don't inflict any health level damage unless the vampire specifically chooses otherwise. They're outlets for blood created with deliberate effort, not random damage. Vampires who know Black Metamorphosis and more advanced powers may choose to go ahead and inflict ghastly wounds like ragged rips through their limbs or their own chest, which the emerging shadow heals on its way into the world. When the effects end, a faint residue of blood may linger.
Powers that don't require blood draw on shadows the vampire ejects from herself. The shadows may flow out of her open mouth or even emerge from shadowed folds in her clothing. When the effect ends, the shadows draw back into her the same way.
Abyss
Most vampiric powers affect either the vampire himself or the surrounding material world--mostly the perceptions and mental states of nearby human beings. Like necromances and thaumaturges, vampires using Obtenebration reach outside the world into a different sort of space and bring back dark gifts with them.
For many Obtenebration practitioners, the Abyss is simply the conceptual realm from which they draw shadow-stuff. A handful of Lasombra probe deeper, finding layer upon layer of mystery in that endless blackness. Intelligience exists in the Abyss. It does not possess self-awareness or even identity in any comprehensible sense. Fragments of knowledge and passion come together for a time, then break apart. The mind within the Abyss is in some ways more like a computer capable of emotion as well as logic then a sentient entity, a pool of resources executing instructions provided by some unknown force.
(Las Cbk Rev)