The first three bosses went down in Normal mode with a little over two hours of actual work - we had some trash wipes to overpulls, and some connection issues, and stopped a bit early for Flex - and then we took another hour to clear through all 4 bosses available in Flex.
There's not much more to say about Immerseous other than that it's the loot-pinyata of this tier. After looking over the journal, I was worried about the Fallen Protectors - it looks extremely complex with 8 NPCs all using different abilities, and I thought, similar to Horridon, it might become a huge stumbling block for Normal mode and more casual guilds. In execution, it was ridiculously simple, we 2-shot it rather easily with three healers and no issues over enrage.
After an absurdly long train of Sha-trash through the Dark Heart of Pandaria scenario space, we came up to Amalgam of Corruption (aka Norushen) and that was the first encounter that required a few eipes and planning and positioning but even that only took two attempts after we swapped in a third healer, though the kill was razor-thin, as the killing blow landed at the same second as the insta-wipe Enrage. But that's more of an optimization issue. Fun times.
Anyway, here are some quick tanking tips:
ImmerseousYou cannot take a Corrosive Blast with the debuff. Just don't do it. Flank him and leave about a 45 degrees gap between you and the other tank. Don't stand in puddles, kill adds, and then collect loot
Fallen ProtectorsLeave Sun Tenderheart alone, she's untankable, one tank should hold Rook Stonetoe next to her for the initial burn to get some good cleave action going, while the other tank kites He around the outer perimeter to drop off poison puddles. The only thing that the Rook tank needs to worry about is positioning so that no one else is hit by Vengeful Strike. The He tank should be careful to avoid Gouge by turning away from the boss or use a CD if you did get hit.
Pro-tip: Glyphed Divine Protection with a 30-second CD thanks to the new Unbreakable Spirit is awesome for both He and Rook. Especially since you can use it while stunned.
Desperate Measures: Rook spawns three adds that should be tanked, keep avoiding Defiled Ground and don't run into Inferno Strike or you'll bring the ground debuff with you. Interrupt Embodied Gloom if you can, and this is a very easy phase. You can't do much to help with He's Measures, but you can provide Hands of Protection and Hands of Sacrifice if the person with the mark needs help. Lastly, Sun's Measures require you to be inside a small dome to avoid taking the raid-wide AoE. You can soak it with chains of CDs but there's no need - position yourself right at the edge with Rook facing you out of the sphere, and no one else will get hit by his frontal cones.
Amalgam of Corruption (aka Norushen)Survive the tanking challenge, tank swap the boss on high stacks of debuff, pick up the big adds, help kill/interrupt/stun small adds when you're not tanking, soak 4 puddles of Residual Corruption each, and dodge the cutter. That's honestly all there is to it. The amount of AoE damage going out is very high, but three healers eased that part of the fight considerably, along with liberal use of Devotion Aura and other raid-wide CDs for casts of Icy Fear sub-40% or so depending on how many CDs you have (Devo, Tranq, HTT, Spirit Link, etc.)
Tanking Challenge: This one is pretty damned simple, once you realize you don't have to kill the add, you just need to survive for one minute. Shield of the Righteous (and I imagine, other Active Mitigation abilities) will diminish most of the physical damage you take. He uses four abilities more or less on cool-down. Most dangerous to least, and what you do:
1. Titanic Smash - 2 second cast spell, can't interrupt. Frontal cone attack. Run through him or strafe well to the side. It hits for 1 million damage (before armor, absorbs, etc.) You can (barely) survive it with ~800k health, but there's no reason to get hit.
2. Hurl Corruption - 2 second cast spell, you need to interrupt it, the cooldown is a second or so longer than your interrupt cooldown so you can get every single one. Make sure you're in range if you're strafing too far for Titanic Smash. If you have it on CD for some reason, Avenger's Shield will do the trick. It hits for ~700k Shadow damage and is painful. Watch the timer and don't get hit.
3. Piercing Corruption - 1 second cast spell, can't interrupt. Physical attack that hits for 600k, Shield of the Righteous makes it very trivial.
4. Burst of Corruption - 2 second cast spell, can't interrupt. 300k health shadow damage AoE. Heal it with WoG/EF or soak it with SS, it's not a problem.
Also, keep using your defensive abilities, it's more important that you survive. No need to save them for later.
One minute of that and you're done.
Sadly, no loot for me so far, but I've only used one coin, as the second and third bosses aren't offering great items for upgrades. But I did finish off my Legendary cloak, and that's pretty awesome. However, it doesn't feel awesome. More of that in a later post, I'm sure.
Anyway, I'm not going to comment about Flex as we it was very late, and we burned through it rather messily with 15 people with eyes drooping. You'll be fine.
Tonight, I'm hoping we make it at least past Galakas - though I secretly hold out hope for killing Iron Juggernaut. Enter the gates of Orgrimmar will be very satisfying.
Good luck. everybody!