In Cold Blood is a Death Knight spec that wraps your enemy in frigid winds and a flurry of heavy strikes. The main reason is due to Might of the Frozen Wastes with Butchery in conjunction with glyphs of Frost Strike and Howling Blast. Chill of the Grave allows you to build up a lot of rune power, up to a maximum of 130 with Runic Power Mastery, for a total of 4 Frost Strikes in rapid succession. In order to gain that rune power, you simply use your Obliterate after having applied your diseases to your foe.
Also, there is a lot of survivability with this spec found in Hungering Cold, Scarlet Fever, Chilblains, On a Pale Horse, and Endless Winter. It’s hard to complain against your enemy dealing 10% less damage, your enemy being stuck for 3 seconds, having 30% shorter duration of slows, and free casting spell disruptions! Also Hungering Cold is always entertaining for survival purposes, especially if it is used after Howling Blast, since Frost Fever won’t break the effect. Also Dark Succor will help replenish any lost life while going in PvE, but for PvP or raiding, you may want Strangulate or Death Grip. The points in the Unholy tree are an interesting choice that are up to you, but are still very important. The 30% extra damage is very handy, however, going with a 12 second longer duration would allow for more uses of Obliterate and Frost Strike without having to reapply your Plague Strike, Howling Blast, or an Outbreak cool down.
As for your rune of choice, if you keep your diseases on your enemies, then your Obliterate will pretty much always deal more damage than your Frost Strike (and I do not know how much Mastery is needed to make Frost Strike surpass it, if it even can). I do know, however, that it is just plain funny using either Razor Ice or Cinder Glacier to further increase the damage of your Frost Strike to make it somewhat close, and be a better form of burst damage. My character is in somewhat decent gear, and my critical hits were for 30-39 thousand damage and each strike was right when the GCD was completed, so I would say that is fast enough damage. Oh, and of course you should be in Frost Presence for the quick build up of rune power and extra frost damage.
For all of these reasons, this spec will help you take down any threat In Cold Blood!