All power demands sacrifice and pain. The universe rewards those willing to spill their life's blood for the promise of power.
Sindri, Alpha Legion Sorcerer, Warhammer 40,000
GG: Whoa. That's neat. I wish I could do that.
Erik: Don't you have the ability to say you have that power then makes it so you have that power or something?
GG: Well not exactly. I can only do that when I'm not exactly doing it on purpose. Because when I do it on purpose, I'll have to pay the price. And I really don't like paying the price.
Erik: Oh... Can I ask what the price is?
GG: Blood and/or physical health. The amount of price is always related to the impact of what I change. But the exchange rate is horrible. Remember when I said I lost the bones from my right hand? That happened after I changed Asagi back into a human. It's always very- Oh, you know what? Let me just show you.
(GG looks at Erik for a moment)
GG: You are orange.
(Erik's green features turn orange and a large cut appears on GG's left Cheek, he bleeds Rainbow-colored blood)
GG: See? I just changed your color and what I got is a nasty cut.
"So much blood, waiting for purpose."
—Blood Lord Vladimir, The Crimson Reaper, League of Legends
While the aristocratic vampire bloodlines bestow potent supernatural powers, some devote themselves to further occult study, honing their magical craft. Cut off from anima as a source of power, they have learned to cannibalise the energies from the stolen blood in their veins. This renders them physically weaker than their earthier kin, emaciating their frames with the purge of every ritual. They claim to require the blood of the magically abled, but this is an affectation rather than a scientific fact.
—The Buzzing, The Secret World
You want? You bleed.
—Nigsu Ga Tesgu, by Jeff Somers