I am not sure if this helps but its from the DK tank strat section of the tanking guide:
Just like normal, I don't recommend DK tanks for bat duty, however we are arguably the best boss tank for this fight due to the heroic only Crystal Shell mechanic. Damage goes through our blood shield before the crystal's shield, so we can use Death Strike before big damage like snapping Bite and Stomp to make sure our crystal shield is up close to 100% of the time. The shield is boosted by healing taken, so if you are low things like VB and Death Pact are fantastic for getting a shield back to strength after taking a bit hit. It is important to know that your blood shields will primarily be minimum strength, since absorbed damage is not factored into the 20% damage calculation, so stamina is much preferred over mastery for this fight since at min DS value it provides more shield per point. "