Originally Posted by
gildelicil
I have been pondering casting Doom in AoE situations. I thought I would add my thoughts to this thread and hopefully get some feedback from people more skilled in Demonology than I. The guideline turns out to be very simple. The maths follow to explain my reasoning.
Suggestion for best practice:
Cast Doom when:
If the number of mobs is fewer than six, and the mobs will live longer than 2 ticks
If there are exactly six mobs, and your crit is higher than 20%
If the number of mobs is more than six and they will live longer than 3 ticks
Doom is an interesting beast. It costs 60 fury to cast it, but you can statistically say it costs (60 - 50*nTicks*critRate), since for each tick of doom, there is a chance of a crit, which spawns an imp which will give you 50 demonic fury over time. It also does approximately about half the damage of the amount of touch of chaos (which costs 40 fury). Void ray (also 40 fury) does about 1/3 of the damage of touch of chaos (ToC). We can use the damage of ToC as a measuring stick.
Also, wild imps deal damage in Firebolts, which do about as much as 1/4 of a ToC. Since they cast 10 of them, they do about 2.5 ToC of damage when they spawn, so the expected imp damage from a doom is (2.5*ToCDamage*nTicks*critRate). To break this down, with 20% crit that gives:
1Tick: 0.5 ToC
2Ticks: 1.0 ToC
3Ticks: 1.5 ToC
4Ticks: 2.0 ToC
So if you have 2 targets, you will want to cast Touch of Chaos if they will die before two ticks (about 30 sec) of Doom since 1 doom tick is worth about 1 ToC (0.5 from tick damage and 0.5 from expected wild imp damage). If they will last 2 ticks, ToC and Doom do the same base damage, but wild imps will give an expected 1 more ToC of damage, so cast Doom because one Doom is worth 2 ToC.
If you have 3 targets, casting void ray and cycling touch of chaos is about sixes, but you might as well use void ray because you don't have to worry about targeting (for keeping Corruption rolling). You don't want to cast Touch of Chaos anymore, but the same maths from before apply, but now with Void Ray. Cast Doom if the add will live through two ticks.
As the numbers of adds increase, the pattern doesn't change much. When you have 6 adds that will last about 1 minute each, Doom has the same damage per cast time as a Void Ray spam, but it's cheaper (thanks to wild imp procs). But with six adds, demonic fury becomes an abundant resource from AoE abilities, so cost isn't as important anymore. The wild imps damage ensures it is worth casting Doom. But the value of two ticks of doom is about 2 ToC casts; this is the same as casting Void Ray on the six mobs. Because there is no guarantee of imps, you probably don't want to cast Doom unless the add will last for three ticks. Theoretically, adding more adds to the mix should make Doom less valuable, but since Doom isn't victim to the Area Damage Cap for AoE abilities (like Void Ray), it will always be worth casting if you can get three ticks out of it.
There is a catch in all this. For the wild imps to matter, you need to have a target to attack. As a boss is about to die, the extra damage from wild imps may not pan out. It takes time to get all those firebolts cast. In most situations, there will be another mob to kill, but it's worth keeping in mind.
Another thing to note is that this also means that Doom scales non-linearly for demonology warlocks with crit because you get to double-dip. Doom can crit (making it hit harder) but it also gives imp procs (with spells which also benefit from crit.) Consequently, the higher your crit rate, the higher the benefits of stacking more of it. Consequently, as the expansion progresses and stats inflate, demonology warlocks may start to favor crit more.
Appendix: Maths for value based on amount of crit
The amount of damage done by a spell based on crit is (1+critRate). If we let ToCBase be the base damage of touch of chaos without crits, the damage of Touch of Chaos with 20% crit is (1+0.2)*ToCBase. So the value of Doom based on ToCBase is 2*ToC+(2.5*ToC*nTicks*CritRate).
Crit Rate Doom Value
0.20 4.800 ToCBase
0.25 5.625 ToCBase
0.30 6.500 ToCBase