I was messing around as BM in my guild's 25 man and I noticed something odd.
After reviewing the fight on World of Logs, I came to the conclusion that while I still took a damage while under the effect of The Beast Within, I was not stunned by Vile Gas. This is not startling considering the definition of Bestial Wrath and other enrage effects. However, I think it might have a distinct advantage during this encounter... with a little micro management. Judging from the logs the last (3rd) Vile gas I received was countered by The Beast Within effect(Bestial Wrath) AFTER I had been targeted and "painted" by the effect of Vile Gas. I also took no damage. So, it seems to me that there is a cushion that makes timing bestial wrath during this encounter even more possible. The time from when fester looks, casts, and you are still able to move and cast for a bit while dark orange/about to puke.
I was fishing the logs trying to think of a better way to represent this, but this is all I could think of.
World of Logs - Real Time Raid Analysis
This is the query for vile gas.
[23:26:43.562] Sulik afflicted by Vile Gas from Festergut
[23:26:45.593] Festergut Vile Gas Sulik 4573
[23:26:47.508] Festergut Vile Gas Sulik 4574
[23:26:49.624] Festergut Vile Gas Sulik 4573
[23:26:49.624] Sulik's Vile Gas fades
[23:27:13.752] Sulik afflicted by Vile Gas from Festergut
[23:27:15.838] Festergut Vile Gas Sulik 4713
[23:27:17.751] Festergut Vile Gas Sulik 4713
[23:27:19.869] Festergut Vile Gas Sulik 4714
[23:27:19.869] Sulik's Vile Gas fades
[23:28:37.338] Sulik afflicted by Vile Gas from Festergut
[23:28:38.254] Sulik's Vile Gas fades
Here is Bestial Wrath
[23:24:20.072] Sulik gains The Beast Within from Sulik
[23:24:30.087] Sulik's The Beast Within fades
[23:25:44.859] Sulik gains The Beast Within from Sulik
[23:25:54.941] Sulik's The Beast Within fades
[23:27:13.667] Sulik gains The Beast Within from Sulik
[23:27:23.656] Sulik's The Beast Within fades
[23:28:38.254] Sulik gains The Beast Within from Sulik
This is the query for Auto-Shot
2nd Vile gas while under the effect of The Beast Within (Bestial Wrath) due to pure RNG
[23:27:11.839] Sulik Auto Shot Festergut 3385
[23:27:13.670] Sulik Auto Shot Festergut *6734*
[23:27:15.838] Sulik Auto Shot Festergut 3728
[23:27:17.751] Sulik Auto Shot Festergut 3884
[23:27:19.869] Sulik Auto Shot Festergut *8712*
[23:27:21.802] Sulik Auto Shot Festergut *8754*
3rd Vile Gas
[23:28:36.895] Sulik Auto Shot Festergut 3995
[23:28:38.527] Sulik Auto Shot Festergut *7543*
[23:28:39.863] Sulik Auto Shot Festergut *8117*
[23:28:41.304] Sulik Auto Shot Festergut 3713
[23:28:42.640] Sulik Auto Shot Festergut 3932
[23:28:44.088] Sulik Auto Shot Festergut *8203*
[23:28:45.526] Sulik Auto Shot Festergut 3662
[23:28:46.814] Sulik Auto Shot Festergut 3658
I am not 100% sure but it seems to make sense, any input would be appreciated.