One of the core mechanics of the Death Knight is their reliance upon diseases and they are currently the only player class to be based around their frequent use.

Many of a Death Knights attacks become more effective the more diseases they have placed upon their target but only the Death Knights own diseases will cause this scaling effect; the attacks will not benefit from other player created or various item based diseases.

The two basic diseases a Death Knight has access to are Frost Fever which is applied at range by the Icy Touch spell and Blood Plague which is applied by Plague Strike.

Both diseases deal damage over time to the target and have a secondary effect; Frost Fever slows down the targets attack speeds while Blood Plague has a chance per damage tick of removing a heal over time effect that is on the target.

In addition to these two basic diseases, a third disease can be gained by talenting into the Unholy tree and picking up Crypt Fever. This third disease is automatically placed on the target when you apply either Frost Fever or Blood Plague and acts to increase the damage of all diseases on the target by 30%. Crypt Fever can be further improved by talents, turning it into the Ebon Plague which increases the damage the target takes from any source of magic by 13% in addition to its old effect.

Most of the Death Knights primary damaging attacks all increase in damage by a fixed amount per disease on the target making it important no matter what your spec is to keep your diseases up on your target at all times; generally the first attacks you will ever make when fighting will be Icy Touch or Plague Strike.

The big exception to this is Death Knights who talent heavily into their Frost tree; many of the talented attacks gained such as Howling Blast do not scale with diseases but instead only increase in damage when Frost Fever is upon the target; this allows them to ignore Blood Plague for the most part, giving a little more flexibility.

The most important attack that is reliant upon your diseases however is Death Strike which heals you for a percentage of its damage, dependent upon the number of diseases active on the target. Without any diseases active, your Death Strike will not heal, but when there are diseases present you will gain 100% of the damage as healing along with an additional 50% for each disease on the target.

With one disease active you will heal for 150% of the strikes damage, all three diseases will yield a 250% heal effect; this is especially important to remember while levelling as the healing provided by Death Strike allows a Death Knight to solo without any down time and with a little care makes you more than capable of successfully taking on many of the game’s elite monsters by yourself.

Due to this reliance upon diseases, a Death Knight can be severely reduced in effectiveness in PvP when fighting against classes with dispel mechanics, making a Shamans disease cleansing totem their natural bane, especially since in order to reapply the diseases, additional runes must be expended, preventing Death Knights from utilising their big attacks