Guardian Druids' Mastery (Nature's Guardian) has been replaced with a new Mastery: Primal Tenacity.
Mastery: Primal Tenacity causes the Druid to gain a Physical absorb shield equal to 16% of the attack's damage when they are hit by a Physical attack. Attacks which this effect fully or partially absorbs cannot trigger Primal Tenacity.
First I would like to say I'm glad they are changing the mastery. Just a static armor increase was lazy and incredibly weak compared to other secondary stats.
That being said, I have a strong feeling Primal Tenacity will not stay in it's first pass. Yes the absorb is great and I like the whole idea behind the new mastery, but let me give you an example to explain how it doesn't work well with the druid kit.
I'm tanking one mob, say Garrosh phase 2. Just the boss's melee attacks as incoming physical damage.
Sequence of events goes as follows:
Garrosh melee's Tova for 200 000
Tova gains Primal Tenacity (50000 absorb)
Tova gains Tooth and Claw
Tova casts Maul
Garrosh receives Tooth and Claw debuff (reduces next melee attack by 165 000)
Garrosh melees Tova for 40 000 (Not enough to break my Primal Tenacity shield 5000 left)
In this event I have not broken my Primal Tenacity shield and therefore do not get a new one. Next melee is going to hit me almost full and I will not gain a new shield.
My first dreadful feeling from this is, I'm going to have to have a weakaura tracking my Primal Tenacity shield strength and a Primal Tenacity cancelaura macro in order to min/max...
Let's just hope some fine tuning comes to this.