MOUNTS

Death Knights have access to two class mounts, one ground mount and one flying mount, here are guides to getting both:

You obtain the quest from Salanar the Horseman who paces around Death's Breach. The quest is called Grand Theft Palamino which requires you to go to the Havenshire Stables and steal a horse then ride it back to Salanar. Salanar will then transport the Horse to "The Realm of Shadows". Salanar then gives out the next quest in the line named Into The Realm of Shadows. Once you accept the quest, Salanar will teleport you to The Realm of Shadows,which looks like a more grayer version of the world. You must find a Dark Rider,slay him and take his horse back to Salanar (Who you can still see) You will be brought back to the real world and Salanar will reward you with Sigil of the Dark Rider and teach Summon Deathcharger.

The flying mount is simply bought from a vendor called Dread CommanderThalanor in Acherus Hold for 950 gold. The mount is a scaling mount, so whatever your riding skill is it will match it and fly at the appropriate speed. You will still need to buy your flying skill unfortunately