Go for improved Mangle!

Synopsis
Is it better to get improved mangle or master shapeshifter? With Idol of the corruptor; I think so. iMangle here I come!

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Today I just thought of this when I saw the following item on wowhead. Idol of the Corruptor.

As if it was it's destiny, today we got General Vezax down. And guess what he dropped. And guess who got the item. Yep yours truly has the idol now. Now I don't have the time to do this at some point, but I have to do it now, tomorrow Ulduar is waiting again. (Btw more on the Vezax fight later. It is a really nice druid cat fight).

I tested it very shortly, just before we went Yogg-Saron. I did it on cat, and it has no cooldown and a very high proc rate. I guess it is a copy of Idol of Terror, but then with way higher stats. Also there is no cooldown what soever. I think the Idol of terror used to have one. The duration is also 12 seconds and not 10.

Ok so we know it is nice. The thing is, is it worth it taking iMangle for it?

The proc rate for me calculating miss is 61.5%. (see math block 1 below).

With this we can calculate the uptime on a 6 sec cycle and on a 4.5 sec cycle with a 12 seconds duration. This is a really complex thing. I did an attempt to it (see math block 2 and 3 below). If you have real math send it my way!
6 second cycle:
9.1% downtime.

4.5 second cycle:
4.2% downtime.

The difference is 4.9%

Now simplified; (It is late):
What does it give: 2.44% dodge and 1.98% crit for me.
4.9% extra downtime comes to 0.12% dodge and 0.10% crit.
In bossfights you have to consider the fact that you will be not able to dps some time. Meaning the buff drops often. The sooner it can be up the better. It is a stab in the dark but I would double those values. Then it is pretty significant.

For iMangle we would sacrifice Shapshifter and Master Shapeshifter. You dont want to drop anything else really.
2 points in Master Shapeshifter give 4% damage done = 4% threat.

iMangle gives threat back in a dps cycle. Taking a quick look at an old post by Kalon we can see that iMangle does 2.8% more threat.
I don't now how valid the stats currently are. But I want to believe that what he posted then is in general true.

In total we would loose 1.2% threat and gain dodge and a bit more SD.
Also we can go back to 5/5 furor which is really nice since you can't always choose the moment the pull is gonna be. Having a 100% certain 10 rage can avoid some nasty stuff.

As I have seldom threat issues I am willing to trade the threat for some extra dodge, especially when progressing in Ulduar. This will be my spec as of tomorrow: Link


Below you will find the math I used to calculate the values as mentioned in Block 1, 2 and 3.

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Math Block 1
First of all the proc rate. Idol of Terror is said to have 68% proc rate (wowhead.com) I did a quick test on a lvl 83 target dummy. For me I got 52 procs in 51 hits, 28 crits and 6 misses. On hit/crit for me that comes down to 52 / (51 + 28) ~= 66%. So I'll take the 68% as a fact for now.
I also, with current gear, miss 2.33% percent of the time. I get parried (15% cap) 7.25% of the time. So that is a 100 - 2.33 - 7.25 = 90.42% hit chance.
Total percentage of proc = 68% * 90.42% ~= 61.5%. The chance to miss is 38.5%.

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Math Block 2
When it procs it has to be renewed within 6 seconds or 12 seconds. So there are 2 chances not to drop it. The chance it drops is when they both miss = 38.5% ^ 2 = 14.8%
Every time mangle is off cd it can be renewed at 38.5% chance.
1 time: 38.5% ^ 1 = 38.5%
2 time: 38.5% ^ 1 = 14.8%
3 time: 38.5% ^ 1 = 5.7%
4 time: 38.5% ^ 1 = 2.2%
5 time: 38.5% ^ 1 = 0.8%

Now there is a 0.8% is will go to 5 misses.
This means that there is a 2.2% - 0.8% chance = 1.4% chance it will only go to 4 misses. This has been implemented below:

So if it drops is will be down for:
30 seconds 0.8% of the time
24 seconds 1.4% of the time
18 seconds 3.5% of the time.
12 sec 9.1% of the time.
6 sec 23.7% of the time.

Average downtime calculation:
time * percentage
-> 6 * 23.7% + 12 * 9.1% + etc.
-> 6 * 0.237 + 12 * 0.091 + etc.
The result is the average downtime.

Average downtime = 3.72 seconds IF it is down. Chance on that is 14.8% so average downtime with 12 seconds is 3.72 * 14.8% = 0.55 seconds per 6 seconds = 9.1% downtime.

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Math Block 3
When it procs it has to be renewed within 4.5 seconds, or 9 seconds. If not it can be renewed after only a 1.5 second downtime. So there are 2 chances not to drop it.
(Most of the math is the same as in block 2)

So if it drops is will be down for:
19.5 seconds 0.8% of the time
15 seconds 1.4% of the time
10.5 seconds 3.5% of the time.
6 sec 9.1% of the time.
1.5 sec 23.7% of the time.

Average downtime calculation (see block 2)

Average downtime = 1.70 seconds IF it is down. Chance on that is 14.8% so average downtime with 12 seconds is 1.70 * 14.8% = 0.25 seconds per 6 seconds = 4.2% downtime.