Shadow Word: Death
Destroy a minion with an Attack of 5 or more.
If you miss, it leaves a lightning-bolt-shaped scar on your target.
 How to get
Shadow Word: Death x 2 are a reward for raising a priest to level 8.
Shadow Word: Death (SW:D) is a destroy effect that works on any minion with 5 or more Attack. This makes it perfect for removing powerful minions, even titans like Deathwing or Ragnaros. This also makes it an extremely valuable card, and the decision to play it should not be made lightly.
While minions with more than 4 Attack can be destroyed with this card, and minions with less than 3 Attack can be destroyed with Shadow Word: Pain, minions with precisely 4 Attack cannot be destroyed by either card. This tactically includes a number of powerful minions, including uncommon cards such as Ysera. One solution to this is to use a buff such as that from Dark Iron Dwarf to increase the Attack of the enemy minion so as to bring it into the range necessary for Shadow Word: Death. This may waste a useful buff, but can be extremely effective. This can also work with minions with Attack below 4 (given the right buff), if a Shadow Word: Pain is not available.
Shadow Word: Death is a priest spell from World of Warcraft. It is an instant attack that deals Shadow damage that can generally only be used when the target is below 20% health, as a kind of execute ability. Favoured by Shadow priests, the ability also grants these priests a Shadow Orb, a resource used to empower their other attacks.
However, the spell previously had a far wider range of uses. Prior to Mists of Pandaria the spell could be used on any target regardless of their health, but dealt equal damage to the priest as to the target unless the target was killed by it. Shadow priests' Masochism talent previously allowed the ability's self-harming effect to restore 10% of the priest's mana, making its regular use vital to maintaining the priest's mana pool. Its backlash damage also made it extremely useful for breaking crowd control effect such as Polymorph which broke on damage; the server delay between casting the spell and its dealing backlash damage allowing it to break the priest out of the effect if cast at just the right time.
This card's flavor text appears to refer to Harry Potter, who survived the assault of a supposedly unsurvivable spell with only a lightning-shaped scar to show for it.