Once you clear the massive loads of trash that are in your way, you'll come face to face with Beth'tilac. Pick your web and surface team healers, and make sure you have someone glued to your tanks.
I've tried healing the web team and the surface team. After a few attempts, I decided I was better off down in the bottom then I was on the web. One of the issues I ran into was that when I was on the web and dropping through the gap, I would end up disconnecting. It was quite frustrating and was enough for me to just put myself somewhere else and send up another player who wasn't experiencing that issue. I ended up settling with two healers for the web and five healers on the ground.
The encounter is front-loaded with all sorts of adds that the raid needs to deal with. Aggro and threat should never be issues for you. Most of the damage seems to come from the spinners that descend from the web, anyway. Your ranged players should be doing their part and taking them out from a distance as quick as possible to allow for the web team to ascend quickly.
Bonus tip: You can use a variety of taunt effects to lower their platforms and force the spinners onto the ground.
Save your raidwide cooldowns for the final part of the encounter. Try to hold off on using them until her health is at least at approximately 60%. I tried to time mine at around 55% or lower. Once Beth'tilac's health gets sufficiently low enough, I time the next raid-wide cooldown for a tank switch. Then I burn another one every tank switch after that. This helps to reinforce the entire raid, and I get additional insurance on the tanks. Emphasize to the rest of the raid to stack up at one specific point behind the boss (for example, we settled on her rear left leg). With enough raid DPS, the boss will drop without too much difficulty. I'd rank her as a gear check type of encounter.
This encounter is a potential raid buster. The craters alone can completely decimate players. This only happens if you allow it to, though. Since the craters are only ignited by the boss, it becomes really easy for players to see it coming. I understand how it would be a challenge to make sure Lord Rhyolith is being steered in the right direction while ensuring there are no lava streams around you. But this is a big individual effort, because that stuff inflicts 150,000 damage to anyone standing on it when it erupts and explodes. It does an initial 75,000 hit if the stream actually hits you.
One other thing I wanted to mention was that Infernal Rage, a fire elemental, likes to continually pulse. Make sure your players are nowhere near it when Lord Rhyolith summons them.
With two tanks, you'll want one tank focused on Fragment of Rhyolith and the other on Spark of Rhyolith. Whoever is tanking the Spark has to have his healer fairly close enough to keep him alive and yet far enough away to avoid the pulse from the elemental. As a raid healing priest, I'd consider putting a shield on myself and risking a few hits from the pulse to keep the tank alive. Just do it at your own risk. You might have to take a little damage, but it'll be well worth it.
Raid cooldown usage is going to be dynamic and based on fire stacks that your raid may have picked up when Lord Rhyolith runs over volcanoes. Players take an additional 10% fire damage for 14 seconds, and it will continue stacking when he runs into one. If the stacks go above 10, I'd snap off a raid cooldown or two until the debuff stacks wore off. Try to stay near the middle of the island. I noticed not too many volcanoes and craters would spawn there. This allows additional time to dodge the streams of lava and the resulting explosions.
Once you go into the final phase, the fight turns into a straight burn. He isn't going to ignore players anymore. Your tank needs to grab him immediately, while the rest of the healers make sure that he stays alive. It should be smooth sailing from that point on.
Shaman (and maybe paladins) would be jealous. My raid group scored two Eye of Purifications.
Apparently, that's extremely rare.
That's the first two bosses in a nutshell! They're both fun and fairly straightforward bosses to get your feet wet with for the latest raid instance. Take Azeroth ... by fire!
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