Haven't failed a run yet with this comp 

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No Mithrala:

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No Brogni:

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No Mithrala or Brogni:

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A Quinnspired comp, if you will. 

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Got on the Stag/Aniri train after our early comp discussions (and because I was too lazy to gear Helicath) and it got pretty easy. Could probably do a better job with blessings. :)

Been running similar to what you both have here mithrala, iniri, geo, and then demytha or helicath and stag knight or Kimi.

Results are similar now to the speed tune. Can't get anything to 100% winrate. Sit between 75-90% each night always at least lose once wasting energy.

Perhaps share you builds for the non DWJ champs. Could just be some simple "more speed for block champs" or some such. Don't bother with Demytha. Her single turn block damage doesn't pull enough pressure off of healers. She ONLY works in the DWJ version, and it's a fine comp.... but even in the video he admits isn't 100%.

Pretty standard builds/speeds on my block damage champs helicath is 248, I have a tower at 246, demytha at 281 and second one that runs 175 for the dwj comp.

As time goes on I swear this fight got worse. First week or so I was having no problems and my success rate was near 100% but since  has dipped averaging probably 80% although I keep changing out gear and champs.

There is some RNG to this fight as you can't 100% time your damage. The one thing I havnt done is pull in brogni, might play around with him in here. That or keep tweaking with the dwj comp. 

That's what Godseeker is in there for, that RNG aspect. Even if someone gets smacked, or two someones, or even Aniri, she passive revives and then revives the second. Mine is about 220 I believe speed wise.

Helicath at 248 is fine. Mine is 245. My Rosh in those screens is 267. A Brogni would help a lot I think. His reflect plus block debuffs is clutch.

As you can see, I don't even bother with Decrease Speed and it's working just fine.

Hopefully this gives you some ideas though.

Ya I've got aniri a 219 speed lol, and have had her in all my comps as well, best reviver in  imo.

I can try the first team you have which is pretty much what I was doing minus the brogni who I'm not sure why I didn't try yet.

My Brogni is in Bolster, so if he's going down, a bit of Immortal or Regen goes a long way here. 

Does Brimstone trigger boss's passive? 

Yes

My 100% WR is similar to Quinn - Aniri, Geo, Helicath, Mithrala, Stag Knight.

On blue, I swap Stag out for Kimi, but at that point it's not quite 100%. Pretty close though.

Give Occult Brawler slightly more crit rate than Kurzad, and then OB will eat the decrease crit rate instead.

Ya I've been using these same teams, I swear my winrate went down after first couple weeks now. Was near 100% and dropped not sure what I changed. 

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Yep.

But that doesn't matter since we're not relying on keeping a Dec Speed debuff up. :)

Update now that keys reset and I had a chance to use them. I tried with brogni and couldn't get it to work other than one lucky win and went back to the dwj tune, which went 5-1. Game does not want me to get 100% win here.

With helicath being weak affinity he was eating the decrease crit rate, I can't remember but I assume last night was force so my kurzad was eating the decrease crit as there was no weak affinity in the comp. Seems the fix is on force bring a magic champion or just always use a magic champion instead of the suggested occult brawler, not sure who yet but maybe frozen banshee can fill this role with her a2 turned off. Food for thought for anyone else using the dwj comp.

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This has been 100% last 4 days, but I doubt it is never fail... but close enough for me if all affinities with no preset required. 

My winrate is about 95% on auto - i really should look at the mechanics as it is when the boss repeatedly cleanses that i sometimes wipe and i havent even checked to see what triggers it.

Mithrala, yumeko, brogni, godseeker, geo.

THIS may be the answer I've been looking for!  Ty... now to test.

I actually ended up getting my khurzad to 130% crit rate and it solved the issue.

I have not gotten to 100% winrate still but that comes down to damage. If I reset my masteries and dropped warmaster it would get to almost 100% winrate. The only issue present after that is even with over 600 acc khurzad has a chance to get his speed down resisted.