It's been a while since Blood Pact had a foray into Icecrown Citadel, but we can't leave without a look at the king. With the increasing faction buff, more and more people are starting to encounter the final fight of the instance, either for the first time or as a hard mode. I'm not about to try and explain the whole fight; your best bet is to watch our strategy video for that. What I aim to do here is to once again look at the encounter through the filter of our spell book, to see how we can get that little bit more from the fight.
There are two abilities you need to stay aware of in phase one. The most obvious is Necrotic Plague. This is a disease that will one-shot you after five seconds if not cleansed. The trick to managing it is to have it removed from you while you are standing by one of the adds. This makes it jump to them and eventually kill them. So as soon as you are inflicted, you need to run behind the adds. Don't run amongst them or in front; they can easily one-shot you with Shockwave. You only need an add to be closer to you than another player.
I use DeadlyBossMods to let me know when I get the plague (a trumpet announcement wakes me up every time).It's important to not worry about finishing a cast; just move. I also find it useful to have an addon highlight when the plague has been removed. Here I use TellMeWhen. It means I can have a nice big icon on my screen while the debuff is active (this also works even if your combat log, and therefore DBM, fails). The same effect can be achieved with addons like PowerAuras and most buff frame addons.
Managing Necrotic Plague is also the first opportunity to gain a little time by using a Summoning Circle. It would seem logical to have the circle over by the adds so you can get over there more quickly, but this isn't great. For a start, the adds may move (tanks being flighty at times). Secondly, the person assigned to cleansing the debuff might be looking to see someone run out and miss a sneaky lock teleporting. It saves just as much time to have your circle on the ranged group and then when you get the plague you run out, wait for cleanse and teleport back. This also leaves you turned to face Arthas and ready to shoot.
Not a great deal to add to the basic strat for warlocks here. Don't bother with the phase one adds unless the plague has worn off them all; just stay on the Raging Spirits. It's hyper-important not to over-aggro here. While any tank that is on the ball will simply taunt them back off you, that brief moment when they turn around could well mean your whole group is silenced and possibly killed by a Soul Shriek.
You may want to stand on a Circle again for this one, as it's a good idea to run to the tank if a Raging Spirit is about to burst out of you, so they can pick it up more easily. Again, being able to teleport back to position faster means more DPS for you and less chance of being fried by Pain and Suffering (that should so be a warlock spell).
Since your minions have no fear of Remorseless Winter, you might find it a good idea to set them on the Ice Spheres (or your raid leader might ask you to). Rather than having to turn around and look for them, you can save yourself the hassle with a simple macro.
Phase 2/tar Ice Sphere
This is where the demonic circle really comes into its own. Defile is the most dangerous mechanic in this phase but is too unpredictable to be effectively managed with a circle -- better to just learn to run. The Val'kyr are where you can win the day. Generally, the raid group should be bunched up in the middle of the platform so the Val'kyr have a long way to drag their victims -- it's also advisable to have everyone just to one side of center, so all three fly in the same direction. Warlocks are the exception; they should be as close to the edge of the platform as they can be and still nuke the boss. Drop a circle and stand on it. If a Val'kyr swoops in and grabs you, then you should have a short and swift flight to the edge. As they drop you, you can simply teleport back to your place and nuke the bejeezus out of the other Val'kyr.
This ability to defeat the Val'kyr mechanic is truly awesome but isn't unique; hunters can actually Disengage back up if they turn and use it quickly enough. I don't know about mages using Blink; I think it just leaves a mage-shaped imprint on the side of the spire.
Always remember to replace your circle if you have to move for Defile (or simply because the fight has repositioned).
Your position will be determined by the strategy put forward by your raid leader. When the Vile Spirits spawn, you get to show off your fancy, targeted ranged AoE -- Seed of Corruption. Throw as many of these up into the cloud of spirits as you can until they are all dead or you are being chased (then run). Remember to keep an eye out for Defile the whole time.
If you are hit with Harvest Soul, then you will (hopefully) be transferred into Frostmourne. Here you have a choice:Heal Terenas or kill the Spirit Warden. Since bandages aren't all that great, I'd go for the latter if I were you. It is possible to flat-out nuke this fight and simply do more damage to the warden than he does to Terenas in the time. This is hard, though, as he has a real killer spell in Soul Rip (another 'lock spell, surely). This is a channeled spell that does increasing damage over eight seconds. You can and should interrupt the cast. There are a whole host of ways in which you can do this: Spell Lock, Intercept, Shadowfury, Inferno, Demon Charge and maybe more (see comments).
Don't forget your Shadow Ward. There's a lot of shadow damage in this fight and at times, it can start to overwhelm the healers. Minimize the damage incoming from the likes of Infest and Pain and Suffering with your ward and keep a healthstone handy. Shadow Ward doesn't completely absorb the damage from Defile, though, so even with it up you will still cause it to grow if you stray into one. Just don't.
Infest. This is a nasty ability that knocks a chunk of health off everyone and then is an increasing DoT that is only removed when you get over 90% health. You might not even notice it land on you if you have a discipline priest on the raid (if the bubble absorbs the initial hit, then the DoT doesn't stick), but if you have it on you, then don't Life Tap. The healers should quickly top you off -- and if they don't, then pop a stone, clear the debuff and then you can Tap.
Oh yeah, and don't release when he kills you at 10%.
Blood Pact is a weekly column detailing DoTs, demons and all the dastardly deeds done by warlocks. If you're curious about what's new with 'locks since the last patch, check out WoW.com's guide to patch 3.3 or find out what's upcoming in Cataclysm from the BlizzCon 2009: Class Discussion Panel.