Originally Posted by Darieth
I'd seriously advise against choosing not to release either Nether or Slate at the start, because the damage increase from the boss would be too much to cope with for any prolonged period.
The boss' damage, along with his ability to apply the MS effect, is greatly reduced with the activation of the Nether Scion. It's relatively easy to ignore the slate drake until the nether scion is dead and significantly reduce the damage to both tanks and make the use of cooldowns less compulsory.
I'd recommend taking Nether Scion and Whelps in the above situation, having one tank take whelps and boss, and the other take the Nether Scion. Taunting at 5-6 stacks is far more optimal that letting it get as insanely high as 10, which is unnecessarily stressful on healers. Drake tank takes boss, boss tank takes drake.
This will free up your third raid healer to offheal tanks as the flame breath is reduced to pathetic 2.2k ticks.
Nuke down Nether scion while using passive aoe on the whelps, nothing heavy, they die pretty quickly (one hunter spamming multi-shot / explosive trap should be able to bring the whelps down in a similar time to the other 4 hard nuking the Scion)
Once both are dead release slate drake and off-tank him the rest of the fight - a holy paladin can bubble first furious roar, and BoP another healer on the second (if you have a ret / prot paladin they can bop the third healer making it even easier), with tanks using cooldowns to survive the third (and /or fourth). There is absolutely no need to kill the slate drake. Ever