As you can see, the Blood Boil AP scaling has been nerfed almost as much as our Heart Strike damage. Thus the proportion stays roughly the same (at high vengenace levels, +388% basedmg wont make a huge difference).
or short version: If you've been using BB > HS at a certain vengeance level/target number, its gonna be the same now.

The only thing that may change is when you're tanking 3-4 NPCs with low vengeance levels. I'd say BB>HS with 3 and 4 targets, really depends on the vengeance and you may have to check it infight. In the end you still need very high vengeance levels for BB to be superior to HS in a singletarget situation.

The last I checked, AMZ definitely didn't work on shadowy attacks. The damage reduction it provides is an absorb, so the attacks just ingored it.

AMZ does affect the shadow damage from the Shadowy Minions, so maybe thats what you saw?

AMZ doesn't work on shadowy attacks, similar to AMS and our blood shield because they are all absorbs. Tanking Gara'jal in heroic modes requires an adjusted Death Strike playstyle, placing shields on the melee attack before and after each shadowy attack, preventing your voodoo'd raid members from being two shot. Until they change the fight either through a hotfix to make blood shield work on shadowy attacks (don't hold your breath) or just a flat out nerf, this plus proper cooldown mapping (including externals) is pretty much the only way you can safely tank 25H gara. (not sure about 10m, but from what i hear it isn't nearly as big of an issue)

I am very aware on how to tank Heroic Gara'jal as a Blood DK, that is not the topic in question.

From my PoV tanking it the last few evenings, I have yet to seen a spot where AMZ was placed the instant before a Shadowy Attack followed by myself/Voodoo Dolls taking a chunk of damage. Perhaps my eyes are slow, but I will most definitely be checking my combat logs/battle text for more information during the encounter tonight.

Upon browsing my World of Logs attempts, during a very close attempt, I saw no damage intake during all of my Anti-Magic Zone timers; none at all. I suspected that the logs were being stubborn, but alas I will check again tonight.

I was very sure it worked :<

Depends on your playstyle, but if you are following the playstyle i gave above then no. And regardless of your playstyle, effective health is very low of the priority totem pole here, as it doesn't help your voodoo'd raid members at all. Keep enough EH so that you can live, but don't go overboard as this is a very mitigation oriented fight.

As far as avoidance vs mitigation, my playstyle for 25H Gara is very dependent on using Death Strike to control the damage around the shadowy strikes, to make sure that my voodoo partners aren't bursted to death. This means mastery is still VERY important. Avoidance has a certain value here, in that avoidance will work on shadowy attacks and mastery will not, but you can't get enough avoidance to reliably prevent burst damage from a melee+shadow grasp+shadowy attack, making it better to plan for the worst and make sure your partners can survive it by manipulating the damage intake around each shadowy attack with death strike and mastery.

Effective Health is useless on Gara'jal. Your Voodoo Dolls will die long before you will. Avoid Stamina like the plague.

I personally went for a full Mastery build with trinkets offering avoidance on use (Lessons of the Darkmaster and the Brewfest one, whatever that was called) to give me maximum uptime on some sort of avoidance cooldown, as well as warrrior sacs, DRW and IBF. Getting a full stack of Blood Shield before going into tank and good rune management you can have a Blood Shield up for most (if not all) melee attacks.

Also, I could not confirm whether AMZ worked as I thought it did or not. Every time I used it tonight I either dodged or parried the Shadowy Attack, according to MSBT.

AMZ is very useful to mitigate the damage from the adds below, it definitely beats out the other 2 in that tree by a mile. What our blood DK did was instead of using stam flask (useless on this fight) they were using armor/mastery elixirs, but you could obviously change the armor to parry / dodge.

With new changes to Death Strike and Death Siphon. First increase damage by 40% and second has reduced AP scaling it is still better for dps to use 2x Death Siphon than 1x Death Strike?

I hopped in LFR to tripple check in case of stealth changes, AMZ doesn't do anything to the shadowy attacks.

If you're going against Gara'jal as a DK, mastery/avoidance are the only things that will be of any help. Even then, the problem is that the Dolls don't have the EH to reliably take 100% of a Blood DK's damage. On 25 Heroic, the damage you'll do to the dolls is impractical to heal through.

The only way to keep it manageable is stacking damage reduction / raid cool downs. You'd need to keep up about 40% damage reduction the entire time you're tanking to remove the chance of the Dolls being gibbed. However, doing this means you're eating all of the external / raid cool downs. Only Bone Shield, IBF, and Army give any benefit to doll targets. So for the entire time you're tanking without IBF, you'd need an external cooldown.

Actually doing this is incredibly impractical. It means your co-tank will have no external cool downs while tanking, and likely that you've consumed all of the raid cool downs. 25 Heroic Gara'jal is the fight where you want to switch to your alt tank as a Blood DK. Particularly, Monks and Warriors are really good for Doll damage (staggering all the melee attacks, or blocking shadowy attacks and melee).

The AP scaling only went from 40% to 34% I think. It depends on how much vengeance you have, but it should still be better damage wise.

Any of you guys have 4 set bonus already? I just got mine, and it turns out the increased healing from DS does NOT affect blood shield amount. For example, with 143% mastery and DS healing me for 92k I get 120k blood shield, instead of 131K. Needless to say, I'm disappointed. It seemed like a great bonus because of the scaling through mastery, but if it's working as intended right now, then it's worth ~900 mastery. Compared to prot pala 4 set bonus worth ~6k mastery. I didn't find any thread about it anywhere, so I made a ticket and I'll post the answer I get here.
I hope it's a bug, but if it's not, then I will think twice about running with 4 set in the first place, since I can get better itemized offset pieces.