This is the second boss of Trial of the Grand Crusader (TOGC). For the normal mode strategy, refer to: http://www.youtube.com/watch?v=GbOfQTJEuqE
Aside from the usual increased in health and damage, the only change in heroic mode is that the Nether Portals and Infernal Volcanoes can now be targeted and destroyed. Destroying them is top priority as these will continue to spawn Mistress of Pain and Felflame Infernals for as long as they remain alive. The fact that they can now be targeted has both its advantages and disadvantages, and aside from destroying them, the rest of the strategy is quite similar to normal mode.
The advantages of being able to kill the portals and the volcanoes is that destroying them fast enough means less adds spawning compared to normal mode. For the portals, it is entirely possible to destroy them before even a single Mistress spawns, hence greatly trivializing that part of the fight. Killing the volcanoes fast enough will only cause 2 Felflame adds to spawn, compared to 3 in normal mode, again making it easier to deal with.
The disadvantage however, is that the burst damage which could have been used on the adds, is now used on the portals/volcanoes themselves. For the case of Nether Portals, the 4pc T13 rotation could have been used on the Mistress for a smooth kill, but instead is used on the portals, which is good, but there is always a chance that the portal doesn't get destroyed fast enough, causing a Mistress to spawn, and no resources remaining to deal with it (the Shadowfiend most likely would have died to Jaraxxus by this time). It is still entirely possible to kill the Mistress at this point, but it would not only require extra unnecessary time, but also extremely precise execution and RNG. The disadvantage of requiring to destroy the volcanoes is also similar, the extra damage which I could have put on the Felflame adds, is now placed on the volcano itself, meaning that by the time I start to place dots on the adds, I am already down to half health, whereas in normal mode, I could have dotted them up by the time they even reached me.
To conclude, here is how I handled each add phase:
1st Portal phase - Use 4pc T13 to burst down portal before Mistress spawns. Archangel and Bottled Wishes are activated.
1st Volcano phase - Make sure own health is topped up, and 3 shadow orbs ready. Cast 3 - 4 Mind Spikes + Mind Blast + SW:Death + Dispel Magic to destroy volcano and the debuff, Dot adds + Dispersion afterwards
2nd Portal phase - Make sure Archangel, Bottled Wishes and Volcanic potion and 3 shadow orbs are up, then Mind Spike 3 times + Mind Blast should kill it before Mistress spawns.
2nd Volcano phase - Same as 1st Volcano phase
3rd Portal phase - Same as 1st Portal phase
3rd Volcano phase - Same as 1st Volcano phase.