|The subject of this article was removed from World of Warcraft in patch 4.0.1.
|Source information needed!
What is Critical Block
Critical Block gives a percentage chance to double the damage reduction provided by your block. When shields are being used, there are two separate calculations — the block percentage and the damage reduction. First, there is a calculation to see if a block occurs (similar to a parry/dodge). If a block occurs, then a separate calculation determines how much damage is reduced. Critical Block increases the damage reduction by 30%, that is the blocked amount is 60%.
Shield using protection classes have as their mastery, Critical Block. They have a base amount of block, and block obtained from mastery. 179 mastery rating gives a Protection Warrior 1 point of mastery that increases both their block rate and critical block rate by 1.5%. Block still only applies to physical damage. The critical block rate is 8 (the base amount) X 1.5 plus Mastery/179 X 1.5. Mastery here is the mastery shown on the Armory. It appears then that critical block starts out at 12% and block starts out at 32%. Ignoring the Hold the Line talent, one may be able to look at their block chance, and subtract 20% from it to determine their critical block chance.
The Avoidance Cap is 102.4%, when your cumulative Dodge, Parry and Block + 5% Boss miss reach 102.4.
Heroic geared protection warriors in Cataclysm may be able to block cap. Their normal block rate may be 52% which is combined with their Dodge and Parry, say both at 14%, giving them an 85% chance to block, dodge, parry an attack, or has the boss miss them. Combine these stats with their use of Shield Block, and their number is pushed to 110%, above the diminishing returns cap of 102.4%.
Shield Block increases their block chance by 25% for 10 seconds, and has a 30 second cooldown. The above warrior would at at a minimum, block 30% of incoming physical damage with shield block active. Shield Block is a significant cooldown option for them. It could also be used on every cooldown, if it is not needed for spike damage.
Shield block and critical block. Assume a Warrior blocking 60% of attacks. And that they have Dodge of 14.4% and Parry of 15%. Their CTC (Combat Table Coverage) is 60.0+14.4+15.0+5.0 or 94.4% which is 8% short of full CTC. Critical block would be 40%. Using shield block pushes critical block to 40% plus the excess of (25%-8%) which is 57%. This 57% is the critical block chance. The blocks will be some 30% and some 60%. 30% X 43% plus 60% X 57% is 47.1%. The average amount blocked.
What mastery does for a Protection Warrior
Adding mastery when one can only block cap using shield block does this: It increases normal blocks and critical blocks. Critical blocks are less frequent than normal blocks, but significant. The warrior still takes unmitigated hits when shield block is down, but takes less of them, reducing total damage taken.
When the warrior shield blocks and is now above the 102.4 block cap, he pushes unmitigated hits off the table. The more mastery he has, the greater the benefit of shield block. Excess mitigation above the 102.4 diminishing returns cap, is converted to critical block chance. The 60% of damage blocked value, might be said to have exponential growth.
So the same mastery benefits the warrior with or without shield block, and the more one has, the more effective shield block becomes.
Mastery or shield block percentages for the above warrior are not subject to diminishing returns. Dodge and Parry are. If one is trying to reach the 'using shield block - block cap' as easily as possible, Mastery is more efficient at that giving roughly 50% more gain than Dodge or Parry. At the same time, it is increasing critical blocks, which also helps in making the choice between mastery and other attributes.
Increasing critical blocks might be thought of as raising the average blocked amount. Moving its average from 30% towards 60%. Warriors have a 12% base amount of critical block. Mastery adds to that at a rate of: mastery/179 = the additional critical block. So adding mastery does at least 2 things, more blocks, and bigger blocks.
Say a new level 85 warrior is just at the block cap threshold, 77.4%. (102.4 - 25.0). They use shield block, and are at least blocking 30% of damage, with a few critical blocks. Let's say they now add 5% to their block rate reforging to more mastery. They are blocking more and their blocks on average are bigger. When they shield block, that 5% from mastery is now 10% increased critical blocks. This is because when they took their 5% from mastery reforging it added to their critical block rate too. When they shield block now, that 5% they took is now excess mitigation as well. It is added to their critical block rate again. One may argue that from the threshold on, they are getting double benefits to the blocked amount. This explains at least part of the exponential growth mentioned elsewhere on this page.
Raising the average blocked amount (from 30% towards 60%)seems significant, and warriors currently have a 2 for 1 way of doing that, at certain gear levels. How much mastery would be too much? When the warrior is asked to generate more threat and needs expertise and hit. During magic damage fights. In those situations, the warrior may have too much mastery.
The mastery cap may be at 102.4% without shield block. It may be when shield block means all blocks are critical blocks. It is noted that, the damage reduction of a block is .7x. The damage reduction of a critical block is .4x. There is a greater percentage difference between .7x and .4x than between 1.0x and .7x.
What is this critical block cap? For a warrior, 67% block, 15% dodge, 15.5% parry, and the 5% boss miss brings one to the block cap. Subtract 18% of that, the difference between base block and base critical block. You get 49% critical blocks. If it is true that additional mastery adds to both excess caused critical blocks and critical blocks, one can bridge the gap two for one from 49% to 100%. Another 25% block would about do that. Adding 67% and 25% for 92% would bring one to the critical block cap, without procs. Adding 92% block, 15% dodge, 15.5 parry, and 5% gives us: 126.5%. This may be close to the critical block cap for Warriors. Entry level Firelands tanks may have around 87% combined block/dodge/parry/boss miss.
There are many factors to consider. The particular fight or the raid make up. As usual, the tank is advised to be as adaptable as possible.
Comparing Block to Dodge finds that a block generates rage, while a dodge does not. In some fights rage may be an issue.
Gearing a block tank
Mastery is highly valued. The Hellscream's reach trinket a good idea with their high amounts of mastery. The magic resistance one, and the on demand agility one.
Parry and Dodge proc trinkets seem to work with the block cap. Combined with a shield block, they can push you significantly past the block cap, perhaps picking up critical blocks during their use.
Most tanking armor has 2 of 5 stats. Dodge, Parry, Mastery, Expertise, and Hit. You may favor armor that has Mastery and either Dodge or Parry. While hit and expertise are valuable, if survival is your highest priority, the block cap is perhaps the best way to do that.
According to theckhd, 1 mastery rating ~ 7 armor for damage reduction. 1 avoidance rating ~ 6.5 armor for damage reduction at projected avoidance levels for T11.
Reforging and Critical Block
The current thinking on the EJ forums seems to be Mastery > Parry > Dodge for survival. Mastery is taken when possible. Some balance between Dodge and Parry may be good, as both are subject to diminishing returns. Parry is favored a bit over Dodge because of the Hold the Line talent, and the increased damage a Parry provides. Hit and Expertise can be given up if survival is the goal.
A number of warrior tanks have switched to the block meta gem away from the increased armor meta. Some spreadsheet scenarios support this.