Mind Flay: Insanity - Shadow Priest Theorycraft from a Practical Standpoint: Devouring Plague: 1, 2 or 3 Orbs?

Monday, October 21, 2013

Devouring Plague: 1, 2 or 3 Orbs?

We all <3 Devouring Plague, so I want to see if we can use <3 orbs with it. The rule of thumb for Shadow Priests is that you wait until you have 3 orbs before you use Devouring Plague. This is a good rule to start off with. DP's damage increases linearly with the number of orbs you use, so the main thing you're doing by casting it with fewer orbs is casting it needlessly more often, which wastes globals that could be spent channeling our filler, Mind Flay. However, we know from Refreshing Dots for Procs that, if we consider wasted globals to be a loss of mind flay damage, we can sometimes find ways to use those GCDs better than just spamming MF. We're constantly striving to do anything better than Mind Flay, and if we're observant, such as paying attention to what procs we have active, that's often possible. Casting Devouring Plague with fewer than 3 orbs will yield an increase in DPS depending on the procs you have active. How many orbs? How many procs? Let's find out.

As I mentioned, DP (and MF:I) increases linearly with the number of orbs used. GCDs aside, casting DP every time you have one orb is just as good as waiting for 3 orbs every time. Knowing this, let's compare those gcds, in the form of mind flay damage, to the gain we get from casting DP when we have strong procs. After all, it makes sense that if we can cast DP under lots of procs, we'll get more damage out of it. Waiting for 3 orbs and then having to cast it without any procs at all makes those Siege of Orgrimmar bosses laugh at us. Another thing that's essential to take into account here is the difference between haste procs and other procs. DP scales up with haste by adding a tick at certain breakpoints. With other procs, it scales smoothy, but with haste it's a stepped gain rather than a smooth one, and so it needs to be considered differently. If you have any questions or concerns about the following math, feel free to ask! I make mistakes, and a major goal in writing this is to know for myself the correct answers to these questions, too.

As always, you should be using Affdotspriest by the amazing Alae. It allows us to see how strong our procs are in a way that is quick enough to make solid decisions even under the pressure of a raid boss fight.

Non-haste procs comparison:
Casting DP with 1 orb instead of 3 means we're using 2 more GCDs than usual on it (3 casts for every 3 orbs instead of 1 cast). Casting DP with 2 orbs instead of 3 means we're using 1 more GCD than usual on it. We need to compare some buffed MF damage to the increase in DP from the buffs.

Where 'S' is spell power and 'n' is the number of orbs used for DP @ +3 DP breakpoint (14,873 haste),

The formula for Mind Flay damage is: 3147 + 1.5*S
The formula for Devouring Plague damage is: n(1643 + 0.786*S + 9(274 + 0.131*S))

When using 1 orb, we "waste" 2 gcds, which is 1 MF channel. This gives us: d*MF = d*DP-DP. Solving for d, d = -DP/(MF-DP). Plug in the spell damage formulas for MF and DP to get:
d = (4109 + 1.965*S)/(962 + 0.465*S)
When using 2 orbs, we equate the damage to 1/2 a MF channel, and similar math gives us:
d = -2DP/(MF-2DP)  = (16436 + 3.93*S)/(13289 + 6.36*S)

I know you're looking at those formulas and saying, "Sheytan, no matter what value you plug in for S, neither equation's value changes very much at all!." You are absolutely correct. Spell power is practically inconsequential to this, which means that it will be very easy to tell when we should use fewer than 3 orbs because the threshold to do so is static. This is why the below graph basically looks like two horizontal lines. To the graph!

(Click to enlarge)

So clearly, we don't really want to use DP with 1 orb. We just don't see a 425% increase in damage. The only exception would be when the boss is dying before we'll get to use a second orb. Also pretty clearly, using DP with 2 orbs doesn't take much in the way of procs for it to be a DPS gain! That's awesome news, so go out there and use DP a bit more often without fear.

What non-haste procs give us 124% damage and allow us to use DP with 2 orbs when they proc?
I know you don't want to hear it, but it varies from person to person depending on your gear, so you need to do some testing. You can find out easily by going to a target dummy armed with AffDotsPriest. Put SWP on the target and right click buffs until you have only the one you want to see. Tips to make this process easier: uncheck "hide when not in combat" on affdots so it doesn't disappear after a few seconds, and make a /cancelaura macro to remove all of your procs except for the one you want to see, then spam it after casting SWP! For example, in my gear at 563 ilvl, I found that Jade Spirit is 5%, Synapse Springs is 6%, my 549 Breath of the Hydra is 29%, and just 4 stacks of my 561 BBoY is 31%. It may sound tedious, but it'll only take a few minutes. Knowing combinations can be good, too. For instance, I also know that 3 stacks of my 561 BBoY + Jade Spirit is enough.

Okay, but what about my LMG, Bloodlust, etc.?:
Good question. Haste adds ticks to DP, so we're going to have to figure out how many ticks each combination of things adds. This is pretty easy thanks to Twintop's graph on howtopriest or checking the smart breakpoints of AskMrRobot's stat weight calculator.

Again, DP's damage is: n(1643 + 0.786*S + h(274 + 0.131*S)), where n = # of orbs, S = spell power and h = the number of ticks we get from haste. When comparing the increase in DP across various haste procs using the same number of orbs, simply subtract DP with the increased ticks from DP with 9 ticks, since14,873 haste with no buffs gives us +3 (9) ticks. PI/Troll racial gives +4 (10). Lust/LMG gives +5 (11). PI/Troll+Lust/LMG gives +7 (13). For MF, we just take the haste proc's value and multiply it by either a full MF channel for 1 orb DP comparisons or 1/2 a MF channel for 2 orb comparisons.

I am assuming 14,873 haste from gear for these comparisons, but similar methods can be used if you're not there yet or are stacking even more haste. That said, more Graphs!

(Click to Enlarge)

It's not surprising that using DP with 1 orb is, again, a loss in DPS. It suffers from a double whammy - 1 orb means it doesn't get the orb multiplier, and it's also compared against a full MF channel. Casting DP with 2 orbs, on the other hand, isn't much of a gcd loss, and it gets a multiplier on its initial tick in addition to the extra ticks. I had planned to investigate more haste procs, but a trend is clear, and MF will also stop benefiting from haste procs due to the gcd cap. It's possible that this will allow DP with 1 orb to become more viable in some extreme haste proc stacking situations, but I'll leave that up to you all to figure out if you are so determined.

I fully believe that similar effects are the same if you're at 18,215 haste (you can use DP with 2 orbs for haste procs), since the primary variable is spell power. However, given how resounding these results were, and how until current TC becomes more definitive I'm favoring 14,873 haste, I have not looked into it to make sure. If anything, I think that 18,215 haste will favor 2 orbs slightly more, as it hits a higher breakpoint or two with certain haste procs.

If you have trinkets that give non-haste stat procs, go to a dummy and see which ones give you at least a 24% increase in damage. Chances are good that if you have some recent trinkets, though, they'll do this. Remember those, and when they proc, it is totally fine to use DP with 2 orbs if you won't be able to get 3 before the procs fall off. If you have haste procs, it's also going to be worth using DP with 2 orbs when they proc.

One very common time that you will likely find yourself doing this is at the start of a fight when you didn't get a chance to save orbs from trash or grab some from your fellow Tito owners. You should be able to get 2 orbs before your procs fall off, but they'll all be gone before you get a 3rd. Use those two orbs with all of those procs!

Also, keep in mind that this is based on the assumption that you're constantly doing these things. If something needs to die within seconds and you won't get to use 2 orbs, heck, use 1!

If you found this interesting/helpful, or if you have you always wondered if it's better to do ____ when ____, follow me and leave a comment. I love pondering new situations, so maybe the answers to your questions will end up on here!


  1. It appears to me that your calculations are based on a FDCL/mindbender setup as they do not seem to me to incorporate the potential gains or losses from channelling mind flay: insanity during the uptime of DP. Do you think that taking Insanity would increase or decrease the threshold for casting a 2-orb DP? Thanks for your excellent work so far, it has really cleared up a lot for me!

  2. That is a very good question. I recommend using this information the same regardless of which talent you choose in the talent tier. While this post is most complete in analysis for the situation when using FDCL/MB, it can roughly apply to MF:I as well. MF:I also increases linearly with the number of orbs you use. The only complication here is the length of the procs and how much they will affect your MF:I channel. RNG of procs is not possible to predict, and I suppose a bird in the hand is worth 2 in the bush, so to speak. So, take that MF:I with some buffs while you can! Overall, applying this post to MF:I is left in the hands of the RNG gods, but the DP portion of it is still a solid gain, so overall with MF:I it will be a gain as well. Revisions will need to be made if we get back to mostly having ICD procs rather than RPPM procs, though.