Death's Advance

Does not seem to affect your speed while mounted.

This is very useful for PvP, since you attack faster (more burst), less GCD (so you can use your abilities quickly) and some amount of run speed (so you don't get kited as much).

Most of the comments on this page are about what this spell ID used to be, namely Unholy presence. Back in the days when stances were a thing, Death knights had presences as their version. One was a tanking one, one was general dps, and the last one Unholy was plus haste and plus movement speed. For a time the movement speed bonus had been baked into a passive for unholy death knights, but eventually it was entirely removed, and unholy no longer had any mobility advantages over it's fellow death knights.

The current ability is the all spec death's advance. It's not the most speedy of sprint-style effects, but the true bonus is that snares are largely ineffectual against you. Where as some of the strongest snares in the game can bring your speed down to 30 or lower, even the worst snare will never bring you below 70%, or 100% while this is active. The active ability also makes you unable to be forced to move, as much like the name suggests, you are as hard to stop as the advance of death itself. Combined with your death grip, and while it's true other people might be faster than you, you'll still make your way to them at a steady pace, like a terminator.

Formerly this was in fact the talent, with Wraithwalk being baseline but they switched it around. Death knights can combine both talents to be mobile but keep in mind they aren't ever going to be a prime mobile class as part of their fantasy.