How To Improve As Unholy Death Knight — The War Within (11.0.5)

Because you can have 3 Runes recharging at the same time, any time you are holding 4 or more Runes, you are effectively capped on runes and wasting potential Rune regeneration. There is never a point in your play where it would be valuable to not cast anything (unless you are pooling Runic Power and, even then, try to minimize downtime), or where you need more than 3 Runes saved up; always keep 3 Runes on cooldown.

Similarly, every point of Runic Power you generate when already at maximum Runic Power is a fraction of a lost Death Coil or Epidemic. In Single Target, avoid Overcapping Runic Power. In AoE, you cannot avoid it, and it is fine to overcap.

In fights that have burst AoE, you want to plan out your AoE for when adds spawn. One very important thing to incorporate into your rotation is a pooling phase, where you save 60+ Runic Power to immediately cast Epidemic before you use abilities like Death and Decay.

Soul Reaper should be cast off cooldown when the target is below 35% health. It does a significant amount of damage, so do not forget to use it very often in execute phase.

Especially for Mythic+, it is easy to hold cooldowns in anticipation of larger and more difficult packs. It is generally a mistake to do so, though. Try and use your cooldowns as soon as they come up! It sounds easy, but it is a major improvement for many people.

In raiding scenarios, it is crucial to properly align your cooldowns. If they are all used as soon as they come up, they naturally align later in the fight. As soon as you start to delay CDs, you end up delaying further cooldown windows, or just failing to combine CDs at all.