Note: this post is primarily about Blood DPS (though it is also applicable to Frost, which often uses Glyph of Disease).
Rolling diseases is the term used for casting diseases while you have temporary buffs (such as Greatness, Fallen Crusader, Unholy Might, Unholy Force, etc.) that increase your Str/AP and then refreshing those buffed diseases with Glyph of Disease/Pestilence. The way Pestilence works with GoD is in the wording: “Your Pestilence ability now refreshes disease durations on your primary target back to their maximum duration.” Compare this to Glyph of Howling Blast: “Your Howling Blast ability now infects your targets with Frost Fever.” The HB glyph causes HB to apply Frost Fever while GoD allows Pestilence to refresh the diseases already applied to your current target.
Keep in mind that the decision to use Glyph of Disease (over Glyph of Dark Death) depends on how many on use/chance on hit AP/Str procs you have. The major ones you can get are: Darkmoon Card: Greatness, 2p t9, Sigil of Virulence, that sort of thing. The more you have, the better Glyph of Disease will work for you.

But Shop, how can I get all my procs to align?
The short answer is that you can’t. The long answer is that there are a few tricks that can help you set up your procs to align.
1) At the start of your fight, use HS-HS-DS (with the option of BT to get a 3rd HS if Unholy Might doesn’t proc) to get as many procs going as possible, then apply diseases.
2) Download and configure Procodile, an addon that can monitor internal cooldowns (ICD) of buffs (as well as the buffs themselves, but I use other addons to cover that). When you have it set up to track all the ICDs of your buffs, if you don’t get all your buffs up at the start of a fight, you can see in advance if and when multiple proc cooldowns will line up again. Considering how important this can be for your DPS, Procodile is a worthwhile investment.
How does Pestilence fit into your rotation?
If you are spell hit capped, you can wait until the last possible second to refresh your diseases. If you’re not, it’s best to leave yourself at least one GCD before your diseases fall off when you refresh. This way if your Pestilence misses you don’t lose your buffed diseases. Aside from this, fit Pestilence in wherever necessary, and where possible refresh disease right before you use DRW so you don’t waste a GCD on a Pestilence while DRW is up.
The ideal rotation for Blood with GoD is to use the traditional 20 second rotation (IT-PS-DS-HS-HS-DC // DS-HS-HS-HS-HS-DC-DC) and simply cast Pestilence before the 21-second diseases run out. This is, however, in an ideal situation and you should be thinking ahead about what might happen to cause you to be away from the boss. One example is Icehowl: you want buffed diseases to stay up as long as possible but are frequently knocked away from the boss.
Some final tips:
- First priority in your rotation is keeping buffed diseases going; if they fall off it’s not always easy to get them going again
- Know when you will be away from the boss so you can refresh in advance
- Cast Pestilence as little as you can while still keeping diseases up (i.e. don’t refresh halfway through disease timers without a good reason to)

