Beast lore is a hunter spell that allows you to see the perinent stats of any beast. These stats include ac, hp, and most importantly their unmitigated damage range.. Using this, we won't actually have to spend time parsing against mobs to figure this out, we can just beast lore everything and see.
There's basically four spells that all reduce -atk (demoralizing, screech [owl pet skill], scorpid sting, and vindication), and one that obviously increases it (cor). We tested by using various combinations of cor scorpid and demoralizing (ie no vindication). In some cases, screech was tested instead of demoralizing, and the change was interpolated for demoralizing (by multiplying by 204 / 100). I tested to make sure that this interpolation is valid vs. a plaguebat (did it with demoralizing, did it with screech, and found the interpolation matched).
Tests were done with untalented scorpid sting (68str/agi debuff) and demo shout with imp demo 5 (-208atk).
Name Level %ScorpRed %DemoRed %ComboRed Starving Mtn Lion 24 29.17 29.17 29.17 Carrion Lurker 52 19.42 28.16 30.10 Monstrous Plaguebat 58 16.81 25.00 29.74 Razzashi Addler 60* 16.14 24.09 27.95 Razzashi Serpent 60* 16.13 24.05 27.92This is about half the data I have, but it shows the interesting parts.
%ScorpRed is the % dps reduction from Scorpid sting. %Demo for demo, and %Combo for both Demo and Combo combined.
From the data a few things could be gleaned:
There is a cap of the effect at 30%. I have more uninteresting data of in-between levels (24-26 and 52-60) that all show that the %reduction of all effects combined cannot go above 30%. This is interesting, but not terribly surprising by looking at how pets work, roughly 30% of their dps is from their "Attack" value, the rest a base based on the mobtype. This cap does not seem to pertain to thunderclap/tf, as I thunderclapped a mob then demo'd it, and the mob's dmg range went down by the appropriate amount.
Demoralizing shout really isn't % based, but scales in some other manner. The lower spectrum of the parses are showing that demo won't drop dps more than 30%, because presumably that's "taking away more atk than the mob actually has". However the change from epl trash mobs to zg trash mobs shows demoralizing still giving a huge dps reduction, showing that it must scale in some other manner.
It has been suggested that raidmobs have fairly normal stats, and are just transformed via a "damage multiplier", and thus dmg reduction from -atk also goes through this dmg multiplier. This data seems to support it to some degree. However this theory also means that emps really aren't special, just we started noticing it here becuase 20% of 10bazillion (ubs) is a sizeable amount. Every mob tested so far exhibits this 20% melee dmg loss.
The obvious extension to the data would be to test demo/screech on The Beast, magmadar, and chromaggus. The formerly mentioned post says that antecdotally it works on Chromaggus, but using beast lore should be able to give a definitive answer. Unfortunately I have no plans to go anywhere near MC or BWL for the rest of the uh, century, so hopefully someone else can test these, as they can be tested basically mid-raid (beast lore is non-aggro, though it's range is fairly low and dogaggrorange is fairly high).
Some other things that I've found that I'm too lazy to post the data for:
Demoralizing shout and screech stack. Up to the 30% cap that is. I guess this was obvious already (since the two icons stack), but since I've never seen someone suggest screech or really demo shout for any of the "I'm getting one-shotted" threads (other than emps), I guess it's not something widely known.
Imp demoralizing shout is pretty huge. The -atk effects are linear (I tested this when testing the interpolation method), which means the dps loss is sizeable on any mob in which the cap does not play a role. For example a mob with 18% reduction via demo would have a 25% reduction with imp demo, that's kinda a big difference. I guess we knew this too, but again, not terribly widely known.
Also since the atk formula is linear, you can see that using curse of wrecklessness will increase dmg by a sizeable amount, but I guess we sorta knew that too.
Maybe all of this was all widely known already, donno. But atm there seems to be really no excuse for not having demo shout up on every mob, which is why we did these tests, to see if we need to start yelling at the warriors again.