How does the Death knight Combat System work?

Death knights have two resources to manage: runes, and runic power.

Next to your character portrait (the top left corner of your screen, by default), your runic power shows below your health as a light blue energy bar. Below that are six circular-shaped rune icons representing the runes you have available.

Death knights have two unholy runes, two blood runes, and two frost runes. These runes cannot be changed, as was originally the case during early alpha and beta testing.

Each primary ability used by deathknights requires a specific number and type of runes. For example, Plague Strike - which deals weapon damage and applies a disease (DoT effect) to the target - requires one unholy rune.

Runes have a 10 second cooldown after they are used. Some abilities require the use of multiple runes, including differing types of runes.

When a Rune-based ability (such as plague strike) is used, it generates a second resource known as Runic Power. Runic power, like rage, decays over time while out of combat at a rate of 1 runic power per second, and currently builds up to 100 maximum runic power.

The second set of abilities available to death knights consume a specific amount of runic power to cast. Death coil, for example, costs 50 runic power and does either direct shadow damage to an enemy, or heals a friendly undead-only target. Death coil can be used to heal yourself if you use the lichborne ability, which classifies you as undead for 30 seconds, or it can be used to heal your pet ghoul.