Cataclysm offers death knights a slew of changes to class talents and abilities. As with anything pre-release, take all of this with a grain of salt, as it were. Nothing is set in stone and if Blizzard decides to flake, all or none of this could be changed.
NEW DEATH KNIGHT ABILITIES
Outbreak: Outbreak infects the target with both Frost Fever and Blood Plague at no rune cost. This ability allows the Death Knight to apply diseases quickly when he’s switching targets or when his diseases have been dispelled.
Necrotic Strike: Necrotic Strike is a new attack that deals weapon damage and applies a debuff that absorbs an amount of healing based on the damage done. The burst is smaller, but a larger overall amount of healing would be required to bring the target back to full health.
Dark Simulacrum: The Death Knight strikes a target, applying a debuff that allows the him to copy the opponent’s next spell and unleash it. Unlike Spell Reflection, Dark Simulacrum does not cancel the incoming spell. In general, if you can’t reflect it, you won’t be able to copy it either.
RUNE SYSTEM CHANGES
The Rune System changes are meant to help death knights feel less constrained. It will change how runes regenerate, from filling simultaneously to filling sequentially. For example, if you use two Blood runes, then the first rune will fill up before the second one starts to fill up. Essentially, you have three sets of runes filling every 10 seconds instead of six individual runes filling every 10 seconds. (Haste will cause runes to fill faster.)
Blood is being converted into a dedicated tanking tree. In addition to damage reduction and healing absorption (when you heal yourself, you’ll receive an additional effect that absorbs incoming damage), the new Vengeance mechanic is designed to ensure that tank damage output (and threat) doesn’t fall behind as damage-dealing classes improve their gear.
All tanking specs will have Vengeance as their second talent tree passive bonus. Whenever a tank gets hit, Vengeance will grant a stacking
Attack Power buff equal to 5% of the damage done, up to a maximum of 10% of the character’s unbuffed health. For boss encounters, it’s expected that tanks will always have an Attack Power bonus equal to 10% of their health. The 5% and 10% bonuses assume 51 talent points have been put into the Blood tree; these values will be smaller at lower levels.
You only get the Vengeance bonus if you have spent the most talent points in the Blood tree, so you won’t see Frost or Unholy specs running around with it. Vengeance will let Blizzard continue to design tank gear more or less the way they do today; there will be some damage-dealing stats, but the focus is longevity.
Unholy has always had a strong niche with diseases, magic, and command over pets and will stay that way. With the Disease Damage passive bonus, Unholy specs will be able to get more out of their diseases, which are integral to the tree’s play style.
Frost is now dual-wield tree with Frost magic damage and decent crowd control. The Runic Power Generation passive will function as the name implies, and the new rune system will make generating Runic Power more appealing.