Craster's Keep

{t}: Add {b}{b} to your mana pool.
{b}, sacrifice a creature: prevent all damage from
black or green source that would be dealt to you
or the permanents you control.
"I said as much to that Mance Rayder once, when he
come sniffing round. He never listened, no more'n
you crows with your swords and your bloody fires.
That won't help you none when the white cold comes.
Only the gods will help you then. You best get right
with the gods."—Craster