The recent nerf to Dragon Soul with the release of patch 4.3.2 means more players are now within striking distance of Morchok on heroic modes. He's a boss that serves as an execution check for your raiding group more than anything else. If your raid group mastered the art of healing through him on normal, then it should have no problem doing it again on heroic.
Just be prepared to do it twice.
The biggest hard mode change is that Morchok clones himself. His clone has the exact same abilities as Morchok prime, except the timing will be off. Your raid will be splitting in two and pulling the two bosses away from each other. You can envision the fight as two pseudo 10-man groups fighting (or two 5-mans, if you're in a 10-man raiding group).
Come into the raid with six to seven healers, if you're a 25-man raiding group. Actually, I'd consider bringing seven if it's the very first time. For 10-man, it is not uncommon for groups to bring in up to four healers for the first time. You'll need them, due to the amount of damage being dished out to the raid. Ideally, try to insist that when your raid leader splits the raid into two groups, the players will show up in your raid frames in different groups. Having all of the players in group 1 and 2 on one side with groups 3 and 4 on the other can be beneficial. The side that is tanking Morchok is the one that could benefit from the extra healer, as it seems more damage is done on that side.
I strongly recommend bringing in tanks with their four-piece bonuses, because they will be an incredible asset.
After 90%, Morchok creates a clone of himself.
The encounter is going to rely heavily on AoE healing. There will be specific instances when your tank needs to get his health spiked up. Due to the way Stomp works in heroic, the two players closest to Morchok take double the damage. This should be a tank and another player who can a large amount of damage; I strongly recommend using a rogue for that role due to the myriad of survival skills and abilities that they have. Have a healer on each side babysit that player, as well.
Your raid needs to stack up on either side for Stomp mitigation. Once a Resonating Crystal appears, DPS players should hustle over to it, but only after they've taken a Stomp. The explosion of the crystal splits damage between seven players who are close by. I like to time my AoE spells to land just as the raid takes damage from the abilities. Ideally, you don't want healers or tanks within range of that crystal, so it's up to the DPS players to make sure that doesn't happen. However, the occassional dead raider means it might be necessary for a healer to step in temporarily to help absorb a crystal. Be prepared for it.
There are times when players move too early to catch a crystal, resulting in lethal damage for that side because there weren't enough players to soak the ability. I suggest having a healer on each side use a healing cooldown (Divine Hymn, Tranquility or whatever happens to be present) as the raid transitions from a Stomp to a crystal. I always found that to be the other delicate part of the encounter.
The tank takes a fairly decent-sized melee swing right after a Stomp since heroic difficulty increases the physical damage taken by affected players. Make sure the tanks on either side have healers dedicated to spiking them up to full health as quickly as possible. You can probably time a healing spell with a cast time heal and follow it up right after with an instant-cast heal (such as a Flash Heal with a Holy Word: Serenity). Keep a finger over your emergency healing button in case the tank gets dangerously low. Guardian Spirit procs from priests can often occur.
Use a Potion of Concentration and other mana cooldowns during the Black Pool phase after you've successfully made it behind one of the stalagmites. You'll be going through about three to four of these phases, so plan them out accordingly. Depending on your raid strategy and the skill of certain players, it is possible for select classes to stay in and DPS (rogues, for example).
The final phase of the encounter is going to be the most intense. Dropping the boss' health to 20% triggers the Furious buff, when he starts hitting faster and his damage done increases by 20%. Whatever cooldowns used earlier in the fight should be up by now for use again. Don't forget to rely on the additional cooldowns of your non-healers (Rallying Cry from our warrior friends, for example). Chain your tank cooldowns one after the other. You need to be able to give the rest of the raid enough time for them to burst the two bosses down.
Pray that your raid sees multiple drops of Petrified Fungal Heart, quite possibly the best healing neck in the game. In case you're having terrible luck with weapons, the Vagaries of Time mace is enough to help tide you over until you score the awesome mace from Deathwing (Maw of the Dragonlord). Best of luck with the encounter!
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