Bloodthirsty vampire

Bloodthirsty vampire is the nickname given to the mechanic of Vampire cards from the Zendikar block thematically bound together by caring about an opponent having 10 life or less. The mechanic is also referred to as bloodied in reference to the Dungeons & Dragons term referring to a creature or character which only has half of its initial hit points or less left. Sorin Markov is not a card with the bloodied mechanic per se, but singlehandedly enables the bonus.

List of Bloodthirsty Vampire cards:
 * Bloodghast
 * Guul Draz Vampire
 * Ruthless Cullblade
 * Vampire Lacerator

Some cards outside of Zendikar also have this threshold for bonus abilities:
 * Blood Baron of Vizkopa
 * Lurking Jackals