After Grim Batol, Stonecore is probably the second least welcome Heroic to pop up in peoples Random Queue. The thing with this instance is that all the bosses are deceptively simple mechanics wise, in that what you need to do is fairly obvious, but are completely unforgiving within the scope of how they work. If you screw up execution here, you will very likely die quick and messy as each boss has one ability, at least, that will one shot.
Starting off with Corborus, this giant shale worm consists of an above ground and below ground phase. During his above ground phase, he executes two abilities. The first is Dampening Wave, a functionally room wide AoE that does shadow damage and applies a healing absorption effect on everyone in the room. Healers will want to either heal this off each player or dispell it depending on what their abilities lean towards so that they can continue to heal the party effectively. The second is Crystal Barrage, a targeted AoE attack in which Corborus is going to spit shards at the person in question: move out of this. On heroic, Crystal Shards will also spawn quickly upon completion of the "spit". DPS should use ranged means of AoE'ing these down immediately once they solidify because each of them are proximity bombs that will chase anyone they have threat on; exploding for 20K and placing a 25% increased damage debuff on anyone they hit. Because of this, letting these run rampant or trying to melee AoE them will likely result in deaths so killing them with while they're bunched on the spawn zone (hopefully) with everyone clear will maximize your AoE potential and eliminate them in short order.
Periodically Corborus will dive into the ground and his second phase will begin. During this phase you'll need your Tank to scoop up multiple Shale Spider adds that will spawn from small dust clouds so you can effectively burn them down and to keep them from raping DPS and Heals. Complicating this, Corborus will periodically leap out of the ground - the area in which he does so indicated by a large rectangular dust cloud - and insta-gib anyone unfortunate enough to still be standing there. This phase is all about effective mob control by the Tank while everyone avoids the kill zone so you can burn these adds down quickly and, preferably, not have any up when Corborus resurfaces.
From here on out it's just repeating those two phases until Corborus is dead or you've all screwed up; whichever comes first :) One thing I will note as warning though: Corborus is bad for going straight into either Crystal Barrage or Dampening Wave immediately upon surfacing from the ground phase. As a healer, you'd best have everyone with reasonable health coming into that transition - especially if there are adds still up - or you will frequently see people fall.
Moving on, we come to Slabhide. This Slate Dragon will breathe, so don't stand in front of it unless you're tanking, but not tail swipe so you can stand behind it and has three main mechanics you otherwise need to worry about as you go through the phases. As you pull him, the first you need to worry about will be a targeted void zone cast at random party members indicated by a dust cloud "quaking" at their feet. Clear this zone quickly because because lava is going to erupt here dealing damage from the explosion as well as creating a lava pool which will continue to tick off your life points and leave you dead in short order.
Shortly after pulling him, Slabhide will take to the air and begin dropping Stalactites on the raid whose strike points will be indicated by, as you'll see in the hallway before him, dark black circles on the ground. Don't stand in the circles or you die, simple as that. From now on, these Stalactites are both a LoS PITA you want to remain aware of for heals and serve a second purpose tied to the Crystal Barrage ability he will begin executing: they're your shields. Whenever he casts that spell, you want to immediately get one of these between you and the boss to block the attack. Note to Melee and Tanks: none of the Stalactites within his hit box, as indicated by the nice red circle around him, will be effective at doing this so plan to have one outside this to run to.
Much like Corborus, repeat this ground/air cycle a few times and you're moving on.
To where, you ask? Why, Ozruk of course, your next welcoming bundle of one shot abilites!
The first of these is Ground Slam, an announced massive frontal cone attack that will kill anyone in front of him when cast. The Tank should always endeavour to keep Ozruk pointed away from the party until this is announced and then immediately run to Ozruk's rear or side as he raises his fist and prepares to deliver this attack towards where the Tank used to be standing. Failure to clear his frontal cone means the Tank dies and the party wipes. While this is primarily a Tank killer, the rest of the party should remain aware of this ability and move appropriately if, for whatever reason, they find themselves looking face to face with the boss when this is announced.
The second ability that will gib Melee or Tanks is Shatter, a 15 yard AoE that will hit anyone in range for 150K damage - enough to kill any DPS, healer, and most tanks. This will be executed in conjunction with his Paralyze ability. Paralyze does exactly what it says but also applies a DoT that does substantial arcane damage if allowed to run its full cycle. There's only one way to clear this debuff and run out of Shatter without letting this happen and that's through taking damage. You're probably wondering: "How do I take damage if I'm paralyzed Mr Blogger?"... Well, here's where it becomes necessary to get abusive with the boss mechanics folks!. Throughout the fight, Ozruk will execute two self buffs: Elementium Spike Shield and Elementium Bulwark. The Spike Shield primarily places a stacking DoT on Melee and Tanks (although, in theory, anyone could run in and get it), as they attack which will break them out of the spell by default while doing periodic damage (do try to not let this stack too high), so, in theory, as long as your Ranged DPS and Healers stay at 16 yards +, they never need to worry about the Shatter... but then you take full Paralyze damage which also starts to add up... This is where Elementium Bulwark comes in - casters of both the DPS and Healy varieties can take advantage of this spell reflect to cast one of their own (softly hitting), DoTs on themselves to break the Paralyze and mitigate the damage. This is especially handy for Healers because now they can keep healing through the Paralyze instead of watching everyone slowly tick down from the various DoTs that are eating away at them.
The mechanics now covered a bit, this is the sequence you're going to see on heroic: Paralyze (a big green cloud from the boss) -> Casting Shatter (everyone within 15 yards needs to get out now). The Tank needs to execute this while remembering two things: running wildly away from Healers is going to end badly when they're Paralyzed so they can't follow quickly and, secondly, when they pick the boss back up they need to have him facing such that he's not risking a Ground Slam at the party.
As such, properly controlling Ozruk's positioning makes this a very Tank dependent fight; doubly so once you hit 25% health and Ozruk enrages to gain a 50% damage buff. That's a good time to Hero/BL/TW and try to end that phase as quick as possible although don't get cocky - sitting in for a shatter because you're "almost there" is a good way to wipe if you miss the goal posts.
With Ozruk down, your final loving caresses of death will come from High Priestess Azil.
As you pull Azil, you'll enter the first phase of this fight during which there are three mechanics you primarily need to pay attention too. Firstly, small packs of Devout Followers will run in during her ground phase but these are easily managed by the tank and AoE splash damage off the boss if you don't simply run them through Gravity Wells. That is her second ability and is cast on a specific player with a very "traditional" circular purple glowing void zone mechanic; these circles should be cleared before they form into the Wells in question. Unlike other void zones, these can be used to kill these adds and it can be a good idea to have people stand such that you end up building a "wall" of them to eat the much larger packs of Devout Followers that will spawn in her second phase. Her last ability in this phase is Force Grip which she will channel cast on a specific player and does up to 100K damage if allowed to run it's full course. This spell is completely interruptible so this should be done ASAP when cast to minimize damage done.
At the end of each ground phase, Azil will cast Energy Shield, knocking back and dealing 15K damage to anyone within 5 yards, and proceed to fly back up over her alter. Now, two large packs of ~13 Devout Followers will begin charging the room and your "wall" of gravity circles should be abused as much as possible to eat these and keep them manageable. Otherwise, pick them up and burn them down. While you do this, Azil will begin throwing boulders at you with Seismic Shard. Targeting the area where a player was standing, you'll see a dust cloud start rising from the earth where this stone will be thrown and everyone should clear this area or... guess what? You're dead.... As such, dodging those stones takes priority here. After up to 3 waves of adds, Azil will rejoin the fight and you'll return to phase one. Be prepared to interrupt Force Grip as she has a tendency to cast this shortly upon return.
Cycle through ground, air, ground, air, ground and you should be done here... hopefully without too much of a repair bill.