Thunderfury

Sticky post from forums http://forums-en.wow-europe.com/thread.aspx?fn=wow-warrior-en&t=196065&p=1&tmp=1#post196065
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Done by Brissa - original post can be found here http://forums.elitistjerks.com/viewtopic.php?id=7138
or
http://forums-en.wow-europe.com/thread.aspx?fn=wow-dungeons-en&t=78111&p=1&tmp=1#post78111

Thunderfury threat generation - Tanking

As I’m sure most tanks who have either played with a thunderfury or played with someone who has a thunderfury understands the proc generates threat. There is however a question which I have not seen anyone answering, and that is how much threat it is generating.

The TF proc effect can be divided into 3 categories.
1: The damage effect, each time the proc activates the target is hit for 300 damage
2: The speed reduction effect, each time the proc activates the target receives an attack speed debuff.
3: The nature resist reduction effect, each time the proc activates the target and targets surrounding it has its nature resistance reduced.

As we will soon conclude each of these effects generate its own threat.

Using a tank with defiance in defensive stance the damage effect will provide a total of 391 threat 300*0.9*(1.3+0.15) = 391.5
This threat is recognised by KLHT (the threat meter used in the experiments) and is accurately calculated.
The other two effects however do not display in KLHT and that makes us able to determine the threat values for those effects.


The test was conducted with 2 warriors, 1 with thunderfury and 5/5 defiance talents and one without thunderfury and without defiance talents.

The first order of business was thus to make sure that KLHT works properly with defiance.
To do this we needed the TF tank to equip another weapon and do a test which measured the threat level when aggro is transferred from one tank to the other.

We tested this by having the first warrior tank a hederine slayer up to 15000 threat at that time the warrior targeted himself and ceased to attack the target. Now the second warrior engaged the target and built threat until gaining aggro.
The second warrior should gain aggro at a total of 16500 threat (15000*1.1 due to having to generate 10% more threat than the current target of the mob to force an aggro switch) which is exactly what happened.

Knowing that KLHT worked properly for a non TF scenario we could start the real testing.

The first step was to calculate the threat gain from TF on the attacked target.
This was done by the non TF tank tanking a hederine slayer up until 20140 threat and then selecting himself and ceasing to attack the target. Now the TF tank could engage and keep building threat until gaining aggro. Since KLHT recognises the damage effect from thunderfury aggro should be gained at 22154 threat if the other debuffs had no threat generating effect. This was not the case however and the TF tank gained aggro at 19700 threat.
By subtracting the displayed threat from the real threat and counting the TF procs we can calculate the threat generation from a single TF proc.
Real threat > 22154
Displayed threat = 19700
TF procs = 7
Threat per TF proc > (22154-19700)/7 = 350.57 in defensive stance with defiance.

This can be compared to sunder armor giving 377 threat in defensive stance with defiance.
With a proc rate at 25% this constitutes a significant threat increase and its no surprise that mobs tend to stick like glue to tanks with TF. It also raises the question if its viable giving rogues TF due to the massive aggro gain that undoubtedly is better used for a tank.

These 350 threat are however the result of two different effects, the speed reduction and the nr reduction effect. To find out how much each of those two effects contributes we made another test.

The nature resistance reduction is a multi target effect hitting a total max of 5 targets.
We used this by having the TF tank gather up 3 shardtooth maulers and slowly killing two of those with auto attack only leaving the third mauler untouched. This third mauler had during the course of killing the first two received 8 NR debuffs. We now let the stripped down second tank (in the nude in order to maximize precision in our measurements) beat on the bear until gaining aggro. A total of 1900 threat was generated before aggro was transferred to the new tank.
Since aggro was transferred at 1900 threat we know that the threat generated from the 8 nature debuffs was a total of 1727 or 216 threat per proc with defensive stance and defiance.

Conclusion
The Thunderfury proc generates threat in addition to the threat generated by its damage.
The attackspeed debuff on the main target generates 134 threat.
The NR debuff on the target and surrounding targets generate 216 threat.
Threat values used are with defensive stance and defiance and defined by KLHT with sunder armor giving a reference threat value of 377.