Bloodlust - When?

Bloodlust is one of the key abilities that when properly used can greatly ease an encounter. But, since it's only available once per fight (LK Heroic excepted), it needs to be timed properly. There are different views on how to time it. The naive claim is that it should be popped when the boss is below 35% HP, because several classes deal more damage then (the so-called Execute-phase). However, this turns out to be false.

Execute-phase or not
When you Bloodlust in the Execute-phase, the time you spend in this phase goes down, which means that the raid has less time to benefit from that sub-35% DPS boost. It turns out that this effect exactly compensates for the increased damage you get from Bloodlusting during the sub-35% phase. And since math says more than a thousand words, I'll show this.

The following variables are used:
- H = boss HP
- R = base raid DPS without Bloodlust or sub-35% bonus
- D = duration of Bloodlust (40 sec)
- e = raid DPS increase factor due to Execute-phase (1.2 means 20% increase)
- b = raid DPS increase factor due to Bloodlust (1.2 means 20% increase)
- t1 = time from start to the moment the boss hits 35% HP
- t2 = time from the moment the boss hits 35% HP to the moment of death
- t3 = time to kill the boss, so t1 + t2

If we Bloodlust early (say, at the start of the fight), then we have some time with Bloodlust, during which we deal D * R * b damage. So the time left to burn the boss to 35% is (0.65 H - D * R * b) / R. And we need to add D to this to account for the time we spent during Bloodlust. Then we can obtain the time needed to burn the last 35%: (0.35 H) / (e R). Adding this up gives the total time:



If we Bloodlust when we hit 35%, the calculations follow the same idea:



Notice anything special? Right, both results are the same. The conclusion is that whether you Bloodlust early or late, the time-to-kill remains the same.

So when do I use Bloodlust?
Seeing as there is no DPS-gain from waiting for 35% to Bloodlust, I can give some compelling arguments to Bloodlust as early as possible, once all the relevant debuffs are up and people have their rotation going. This way players can pop their trinkets and cooldowns early and automatically have them sync up with Bloodlust, which is a decent DPS gain. If you postpone Bloodlust until the 35% phase, people will either not have their cooldowns available or they will have postponed using those cooldowns, which makes them get less benefit from them over the entire fight.

Another reason to Bloodlust early is that people die from time to time. Especially on new bosses, where DPS actually matters, you may lose people during the fight. At the start, everyone is alive and at full capacity, so you get the maximum out of your Bloodlust.

Decision-altering circumstances
All the conclusions made earlier assume a simple tank-and-spank bossfight with no adds or different phases. This is not entirely realistic and in actual fights, there may be circumstances that make you want to adjust your Bloodlust timing.

Encounter-specific damage buffs (such as Icehowls stun) are a great thing to combine with Bloodlust. A dangerous wave of adds is more easily disposed with a Bloodlusted raid. And finally, don't forget the healers: Bloodlust makes their work easier too, so if you anticipate a period of very high raid damage, Bloodlust can help the healers get through it.

ICC Boss-Bloodlust Guide
A quick summary of when to Bloodlust (IMO) on ICC fights:

- Lord Marrowgar: Preferably shortly after the pull or after the first Bonestorm.
- Lady Deathwhisper: Start of phase 2. Alternatively, during phase 1 after clearing up an add-wave.
- Gunship Battle: People Bloodlust here?
- Deathbringer Saurfang: At his 30% Frenzy. This phase is the most dangerous, so you want to get it over with quickly.
- Rotface: Just after the pull, people will be busy running around to drop their oozes later on.
- Festergut: Just after the first tank-switch. The old tank will be DPSing with alot of damamge-increasing buffs and Festergut will hit 3 stacks of Inhale Blight, causing alot of damage to be healed.
- Professor Putricide: At the start of phase 3 (normal mode) or during the second double-ooze transition phase (heroic mode)
- Blood Prince Council: Once Taldaram or Keleseth gets empowered. Empowered Valanar requires too much movement.
- Blood Queen Lana'thel: At the end of the fight, just after the last round of bites and after the second fear/airphase. More vampires means more DPS.
- Valithria Dreamwalker: Your healers decide, but generally once they have high stacks of their buff and just after they exit a portal.
- Sindragosa: Phase 1. We like to stress that Phase 3 is not a DPS race and just maximize the time we have for that phase by getting through the first 65% of her health quickly.
- Lich King: Second transition phase (normal) or right at the start and again in Phase 3 (heroic).

The non-linearity of the ICC zone-buff

Today (or yesterday, depending on which continent your WoW servers are) the ICC zone-buff was increased from 10% to 15%. That's an increase of your DPS, HPS and HP by 4.5%. I think that the main benefit of this buff is the DPS component, not only does it affect more people, but 4.5% more HP or HPS doesn't drastically alter your ability to survive poorly handled boss-abilities. Sure, there may be borderline cases where those few percent are enough to save you, but in general that Malleable Goo or Vengeful Shade will kill you just as hard today as it did last week.

So why then does this not apply to DPS in the same way? Knocking a few percent of the duration of a 5 minute fight is not a major difference. Except for two things. The first is the enrage timer. On heroic modes, enrage timers on some bosses are a real threat. Especially since we typically have someone die here and there, bosses like Festergut and Blood Queen can end up being close calls, especially on earlier kills.

The time-based add-spawn mechanic
The second effect is far more interesting. Quite a few boss-encounters involve some type of spawns or secondary targets that need to be killed. These spawns are almost always on a fixed timer. In ICC we have Marrowgar (bonespikes), Deathwhisper (cultists), Saurfang (blood beasts), Putricide (oozes) and the Lich King (val'kyr, vile spirits). I've skipped over Gunship and Valithria because the "boss-kill" mechanics are very different from the regular boss-encounter.

Now, with this type of add-spawning, you will have to divert your DPS to the adds before going back to the boss. And this is where the fun kicks in: Higher DPS means the adds go down more quickly and you spend more time on the boss with your higher DPS. The effect of a DPS-increase on your effective boss-DPS (which is what determines the length of the fight) is amplified by the fact that there are periodic adds that need to be killed.

Enough talk, let there be math!
Assume a boss with B HP. Let R denote the raid DPS on the boss and f R the raid DPS on the adds (In case of single-target adds 0 < f < 1, as you lose DPS by swapping to an unbuffed target and having to ramp up your rotation. For AoE adds, f can be larger than 1.). We have adds with a total of A HP spawning every Ta seconds.

To kill the adds, we need A / (f R) seconds, which leaves us with Tb = Ta - A / (f R) seconds to DPS the boss per wave of adds (Pro-tip: If Tb < 0 then you're doing it wrong). Divide by the interval between two waves, Ta and we obtain the fraction of time we can spend on the boss:
1 - A / (f R Ta)
Multiply by raid DPS on the boss to find the effective raid DPS on the boss:
R - R A / (f R Ta) = R - A / f Ta

Not a big surprise, eh? If you have adds with a total of 300K HP spawn every 30 seconds, your effective DPS on the boss is lowered by 10K, divided by the DPS-correction-factor caused by the difference in DPS between boss and adds. Could've worked that one out without the whole derivation...

Buffing your DPS
So now we get 5% more DPS from a new ICC buff (Yeah, I know it's actually 4.5% for this weeks change as I said before, but I'll take 5% for simplicity). How does that change our effective boss DPS?
1.05 R - A / f Ta
So the term that adds a positive contribution to effective boss DPS is increased, while the term that adds a negative contribution remains unchanged. The net effect will be a greater positive contribution on effective boss DPS.

An example
Lady Deathwhisper has 6.7M HP on 10-heroic. In phase 2, she will summon a single add every 40 seconds. The add has 176K HP (averaged between a Fanatic and an Adherent). Lets assume that raid DPS is 30K on the boss and 20K on the adds (So f = 0.667). Your effective boss DPS will be 16.8K. Now, add 5% raid DPS (31.5K on boss, 21K on adds). Your effective boss DPS will increase to 18.3K, an increase of about 9%.

This effect becomes more noticable, the more time you spend on adds. The most notable example was pre-30% nerf M'uru (which I never had the pleasure of fighting, unfortunately), where the tuning was so tight that there was very little time to DPS the boss. Small increases in raid DPS had large effects on the time it took to burn the boss down.

Conclusion and take-home message
We've seen a quick analysis of how the commonly used add-spawn mechanic can amplify the effect a DPS increase has on your raids performance. The effect becomes stronger the longer you take to kill the adds. Obviously, there are all kinds of other benefits to having the adds down more quickly (preventing the Val'kyr from dropping your buddies off the ledge in the Lich King encounter is one such benefit), but from a mathematical point of view, the boss DPS effect is the most interesting.

Growl and hit confusion

Growl (and the taunts of the other tank classes) is a funny ability. It being classed as a spell has resulted in a lot of confusion about what you need to hit-cap it. The +8% glyph doesn't decrease the confusion. So time to shed some light on the matter.

A little bit of history
Most of the taunt-hit-confusion arises from the various changes that have been applied in this area over time. Growl (and the other taunts) are classed as spells. Before WotLK, there were 2 types of hit-rating: spell-hit-rating and "regular" hit-rating. The regular version applied to physical attacks: melee attacks and hunter shots. Spells and physical attacks had a different cap: back then it was 17% for spells and 9% for physical attacks against raid bosses. Growl was affected by spell-hit-rating and you'd need 16% spell-hit to cap Growl (back then you always had a minimum of 1% chance to miss with spells).

In patch 2.3, Growl was changed to be affected by regular hit rating. However, the rest of the mechanics didn't change: You still needed 16% hit to cap it (keeping the 1% minimum miss chance). The only change was that instead of spell-hit-rating, it was now regular hit-rating that did the trick. This was useful, of course, since regular hit-rating was found on tank gear, where spell-hit-rating was not.

With patch 3.0 and WotLK, both flavours of hit-rating were merged into a single stat we now know and love as hit-rating. However, Growl remained a spell with all its properties. And even though both spells and physical attacks use the same hit-rating now, you need more hit-rating for 1% physical hit than you need for 1% spell hit.

So how is it now?
To never miss a Growl, you need 17% hit. You need 26.23 hit-rating for 1% hit with spells. You can glyph for 8% (210 rating), get a Draenei aura for 1% (26 rating) and get a Shadow Priest or Moonkin to debuff the boss for 3% (79 rating). So that leads to the following numbers:

Glyph/Buffs	Rating needed for taunt-hit-cap
None	446
Glyph	236
Glyph + Moonkin/SPriest	157
Glyph + Moonkin/SPriest + Draenei	131

The thing you can control yourself is the glyph, you can (and should!) swap this one in for any fight where a successful taunt is required. With the glyph, you need less hit-rating than you would need for the regular melee cap of 263. In a 25man raid where a Moonkin or Shadow Priest is pretty much garantueed, you can quite easily hit-cap on Growl already.

Conclusion
Due to the Growls spell-character, you don't need to be at the regular melee hit-cap to never miss a taunt. With the glyph, a lower value suffices. I would like for Blizzard to fix these oddities in Cataclysm, they seem to want to make stats easier to figure out and this is one area where some shrouds of mystery can be lifted.