Mythbuster: The Great Immolate Debate

Myth: Including Immolate in your cast sequence increases your DPS?

Let me start by stating this up front - if you're not a warlock, move along, there's nothing to see here.

Still here? Ok, if you are any spec other than Shadow Mage, the answer is and always has been a definitive yes, you should always include Immolate in your cast rotation. The only spec that this is a question for should be the shadow mage, and I've touched on this before - only the shadow mage should have questions about whether casting something outside of shadow damage is worthwhile. Still, if you want some basis for that statement, read on, the numbers are coming, but understand that result would be even more so for you.

Right then, this is a topic that seems to come up every couple of days in the official warlock forums (or some unrelated thread gets hijacked and forced into that zone), and they all look very similar, something like...

Lock A: destruction is just about shadowbolt spamming
Lock B: *sigh* not again - if you're not including immolate you are nerfing your dmg, l2play nublet
Lock C: but i cast immolate once and my dog died
Lock B: well i cast immolate and one-shot most trash
Lock A: i one-shot your mother
Mage : we suck, nerf locks

etc etc etc

Warning - I am going to do some light theorycrafting here - just enough to make the point, not enough to take every calculation into account. Sorry, but it has to happen - if this causes your brain to slowly melt, then feel free to just jump down to the "Conclusion" section at the bottom, you're really not going to miss much, I just want to be thorough.

Setting the Scene:

Straight up, I'm going to ignore spell hit - I'm assuming we're all capped, and that 1% resist isn't enough to sway the figures one way or another. Secondly, I'm going to assume that Improved Shadow Bolt will on average give you a 10% damage increase overall. Due to the nature of how it works, its very hard to put an exact number on it, but 10% seems to get used widely around the web (and its a nice round number). I'll assume this example is in a raid with a fire mage and shadow priest for damage buffs.

In the spirit of keeping things simple, I'll assume 1000 spell damage through gear, and counting talents you have 25% crit. I'll also set this up as a raid environment with an accomplished Fire Mage (one that can keep the Improved Scorch debuff up) and a Shadow Priest (to keep Shadow Weaving and Misery up).

Lastly, spell damage coefficients - each spell you cast has an assigned multiplier applied to your total spell damage, according to a whacky formula. I'm just going to cheat and steal it directly from wowwiki here. All Shadow Mages must have Shadow and Flame Rank 5.

• Shadow Bolt
  

SB Average Damage Base: 572
Bonus Damage from Gear: 1000 x 105.71% = 1057
Succy Sac'ed = 15% bonus to Dmg
CoS = 10% Dmg Bonus
Improved Shadow Bolt Average = 10% Bonus
Cast Time = 2.5 secs

Total Damage = (SB Average + Bonus From Gear) x Succy Sac x CoS x ISB Avg x Crit x Shadow Weaving x Misery
Total Damage = (572 + 1057) x 1.15 x 1.1 x 1.1 x 1.25 x 1.1 x 1.05
Total Damage (average) = 3273

Total Shadow Bolt DPCT = 3273 / 2.5 = 1309

• Immolate

Direct Dmg Base: 327
Direct Dmg Gear Bonus: 1000 x 20% = 200
CoE: 10% Dmg Bonus
Total Direct Damage = (Direct Dmg Base + Gear Bonus) x CoE x Crit x Misery x Imp Scorch
Total Direct Damage = (327 + 200) x 1.1 x 1.25 x 1.05 x 1.15 = 875

DoT Dmg Base: 615
DoT Dmg Gear Bonus: 1000 x 65% = 650
CoE: 10% Dmg Bonus
Total DoT Dmg: (DoT Dmg Base + Gear Bonus) x CoE x Misery x Imp Scorch
Total DoT Dmg: (615 + 650) x 1.1 x 1.05 x 1.15 = 1681

Total Dmg: 875 + 1681 = 2556
Cast Time: 1.5 sec
Total Immolate DPCT: 2556 / 1.5 = 1704

Lets pretend for the sake of argument that you're the only lock in the raid so there's no CoE, and your only mage is a frosty. The maths still looks like this:
((327 + 200)x1.25+1265) x 1.05 = 2020
Total DPS: 2020 / 1.5 = 1346 dpct

Conclusion: Myth Confirmed!

The numbers speak for themselves - casting Immolate in a full raid buffed environment and letting its DoT component run the full length results in 1704 dpct, compared to Shadow Bolt's 1309 dpct. It is worth noting the difference in not having CoE and Improved Scorch up - 1346 dpct vs 1309 dpct; in which case its a very close call (meaning - make sure you give your mage the time to get their Improved Scorch debuffs up first, don't start your cast rotation with this).

Note that Shadow Mage cookie cutter builds don't have Improved Immolate or Emberstorm - both of these talents will skew the results even more in favor of Immolate. Also note that the Shadow Mage build is based around crits, and some nights you'll have the dice give you different results to other nights, but over a long enough period of time this should reflect your findings.

Addendum: I know there are many better theory-crafters than I out there, I am at best a rank amateur - if you see some issue with my maths, please let me know.