I don't really see Bone Shield as optimal for Thorim hard. Thorim's (increasingly) fast swing speed and reduced avoidance makes it a pretty bad fight for bone shield, actually. Frost's advantage is in overall higher mitigation and avoidance, plus the fact that IBF will last for an entire unbalancing strike. VB is very strong cooldown here too, since the increased health makes it more likely you'll survive a crit, and the massive incoming dps makes the bonus healing shine as well, not to mention blood's EH advantage. I'd say unholy is the weakest for Thorim.

Honestly, Bone Shield really shines for Iron Council, but aside from that, I don't see it as a huge advantage. I haven't killed Mimiron hard (though I wasn't aware of additional tank burst mechanics that favor bone shield, aside from the now-nerfed plasma blast). I prefer blood for XT, as the self-healing is nice through tantrum, though it's not really a tough tank healing fight; and Vezax easy is hardly worth mentioning. I mean, as I said before, Bone Shield is the strongest of the three cooldowns in most situations, but rarely (Steelbreaker) does that outweigh the stronger overall mitigation/avoidance from frost or higher EH from blood.

Speaking of Thorim, I have been wondering how his Unbalancing Strike would affect IBF, if at all. If it indeed does reduce IBF to a paltry 20%, Glyph of IBF would shine for this encounter.

I assume that it reduces IBF mitigation iff IBF is cast after Unb. Strike has landed. If it is cast before, IBF mitigation may not change, unless the value is updated at certain interval (something akin to our AP derived from Armor value).

Yeah, I can't imagine why you wouldn't simply tank swap here. Since you have to have two tanks for the fight to begin with (one for gauntlet and one or two for the arena) it doesn't make much sense why you wouldn't simply have your other tank taunt Thorim as soon as you get Unbalanced Strike.

I'm not sure I agree with you on Mimiron though. I've done the fight as both Unholy and Blood and found them to be pretty equal. It really depends on your DPS though. If they are a little on the slower side and you expect to get more than 3 plasma blasts, then Unholy is better, because of Bone Shield and AMZ. However, if you expect 3 or less Plasma Blast's then Blood is as good or better for the fight. IBF the first one, AMS and VB the second and the IBF the third. But that is a question of your DPS more than anything.

From my experience tanking Thorim hard mode (pre nerf - or so I say, without the raid wide stacking MC buffs); This is far from feasible. His attack speed increases drastically and Unbalancing Strike is not on his swing timer. Weeks ago when we did this achievement, we were using CDs when unbalancing was about to hit us as a tank. What we did do to make things easier in the beginning is have our other tank (druid) glyph for Barkskin, apparently that prevents critical strikes while barkskin is active. The beginning was never a problem, it was 11-15 stacks that posed issues. Battle rezzes & soulstones were over used for us as we ended up downing the encounter. Unbalancing strikes + another melee hit within the same second were the things that caused issues, so timing IBF during an oncoming unbalancing strike + any trinkets is what really helped us get through this encounter initially, since you CAN dodge/parry/miss the Unbalancing Strike.

I had some jahnkee blood spec that sacrificed a little threat but allowed me to get AoTD to a 10 min CD and using that channel towards the end on an unbalancing strike was full of win.

Although each week now the encounter went from something we did once for the achievement to a now farmed hard mode since the MC stacks and make the encounter a joke.

How is a 50% (in reality it's probably closer to 60%) damage reduction not worth pressing?

He thinks it's 50 damage, not 50%?

He's likely assuming that if you were going to dodge/parry 50% of the time anyways that there's no reason to press it for 50% damage reduction.

Here's why you use Army:

1) Smoother incoming damage. You're shaving a good bit off of every incoming hit instead of taking spike damage like you would using your natural avoidance.
2) Predictable spikes. If you're about to take some large predictable spike of damage that can not be dodged or parried channeling Army is a surefire way to cut the damage when you have no other options. (Ex: Unbalancing Strike, Fusion Punch)
3) Non-physical damage. Dodge and parry only help against physical attacks, but Army will mitigate all incoming damage including non-physical.

It's a powerful tanking ability, but with the long refresh time it's best to save it for just the right time. Using it on a large predictable spike of damage near the end of a fight is probably the best application as a tank.

That being said I would never spec in to reducing the cool down as a Blood tank. You will be gimping yourself far too much. For what Army is good for you won't need it more than once every 20 minutes.

I solo tank 10 man Thorim hard mode because we don't use a tank in the arena, but in 25 man I only tank him about 75% of the time. If it is possible to solo tank now it likely won't be when 3.2 rolls around and IBF becomes a 2 minute cool down. It's just easier when you use the tanking cool downs that the other tank on the fight has instead of wasting them all of phase 2.

Edit: @Grief: I tank hard mode Mimiron as Blood, and during the second Plasma Blast I get wings from a Holy Priest. I have Vampiric Blood up during this one, and after 2 or 3 ticks of Plasma Blast I pop AMS to let the healers catch up. When I do this 90% of the time the wings don't get used. Take that for what you will.

Do you do it as Blood for convenience of not having to respec for a fight or two or because you view Blood as a better choice for the fight?

I've done Mimiron hard mode in 10 man as blood and as frost. They both bring something to the table, but I preferred blood because it was very useful in every phase. Not to mention the 10% AP and hysteria are very nice for beating the enrage timer.

We had a disc priest who would Pain Supp the 2nd plasma blast. IBF the 1st and 3rd obviously, and if you hit a fourth, well expect to have problems beating the enrage. The blast has also been nerfed once since our first firefighter kill, so maybe a smaller cooldown (VB + AMS) is enough to survive the 2nd plasma.

I really found DRM to be useful in phase 3, to pick up all of the adds and to get the most threat possible on them in case of a bad silence (which no longer happens on 10..and reduced in 25).

This was discussed briefly, but I was talking about 10m, where I tank Thorim the whole time. I hadn't really thought about it, but I suppose the healers have an easier time spamming me between raid healing than they would dealing with tank swaps. I don't tank 25m Thorim, but we do tank swap there; I agree with those who suggested that not swapping tanks gives a high likelihood of the tank getting effectively one-shot.

I'll add one more point about VB since you seem to be equating it with a 7.5k heal. If it increased health and healing taken by 15% both, it would be very similar to an ability that reduced damage taken by 13%. The differences would be the start/end behavior, since you gain the health at the start and potentially lose health when it ends, and vs. abilities like tantrum that deal a percentage of maximum health). The initial heal has a strong value as an emergency button that IBF, BS, and UA lack, and the stronger healing taken is nearly as good as further damage reduction for situations where you're not getting killed--your healers are healing you as if you took 26% less damage. Tack on its guaranteed 30s duration, and I think it's quite reasonable to call it at least as strong as bone shield in many situations and always better than UA.