Special thanks to Nhani for lending me the picture.
Okay, second attempt. After advice from Seri, I'm writing in Google Docs, and then copy+pasting into Blogspot. Phew... Keep thinking calm thoughts.
Death Knight survival guide
The first step towards defeating your enemy is to "Know thy enemy". Thus, here's a crash course to DKs for healers, with counter-advice rolled in. Terms to notice: DK = Death Knight. Core = abilitiy all DKs have. RP = Runic Power.
DKs have two types of resources: Runes and Runic Power. Almost all of their abilities cost runes or resources. None cost both. Some special abilities are free. From "idle", a DK has six runes and no runic power. Using abilities which require runes generate runic power. There's also a very common talent called Butchery which slowly generates runic power while in combat.
When a DK uses an ability which costs them a rune, the rune is put on cooldown for 10 seconds. Among the runes, there are three basic types: Blood, Frost, Unholy. An idle DK has 2 of each rune ready. There's also a fourth type of rune, Death Rune, which counts as any of the other. Death Runes are "converted" from other runes using either the core ability Blood Tap (notice the health cost) or through one of the Death Rune-generating talents, of which there are one in each tree. Blood: Death Rune Mastery, Frost: Blood of the North and Unholy: Reaping. Notice that these talents are "passive" in the sense that they work when you use some other ability. Further, all of these active abilities are melee-attacks, meaning the DK has to be in melee to convert other runes to death runes.
Why is this important? Here's the trick: Since each rune has a 10 sec cooldown, they can usually an ability requiring a certain rune twice before having to wait for the runes to come off cooldowns, and then they can't use other abilities which cost the same rune. I'll show in a moment which abilities this is most critical for.
There's also another ability to watch out for: Empower Rune Weapon. 5 min cooldown... but in PVP, you're bound to see it often.
Like a warrior has stances, a DK has presences. Like a warrior, you have no way of knowing which presence a DK is in unless you see him change it. The three presences are Blood, Frost (aka the tanking presence), and Unholy. Since it costs a rune to change presences and all abilities are usable from all presences, you'll see less stance-dancing than with warriors. In PVP, virtually every DK will use Blood or Unholy presence. The only thing we can really use from knowning this is that they have 1 sec GCD (like a rogue or a feral kitten) while in Unholy presence, which means that you can think of them like rogues in how often they interrupt your spells. Trading GCDs with them only works if they're in blood presence, otherwise you can't out-GCD them.
DKs are based around the concept of diseases. A lot of their abilities deal additional damage based on the number of diseases the DK has on you. Note that only the DKs own diseases count, so two DKs or a feral kitties doesn't drastically improve a DKs damage. Good thing 75% of all healing classes can remove diseases... sorry, druids, DKs are meant to be your counter.
The two basic diseases a DK has is Blood Plague and Frost Fever. Unholy DKs also have an additional disease, called Crypt Fever/Ebon Plague. Almost all Unholy DKs will invest enough talent points to get the last disease, which is better. Notice that this last disease always comes with one of the first two. That means; if you remove the first two diseases, you also loose Ebon Plague.
The ability which applies Blood Plague is called Plague Strike. The core ability which applies Frost Fever is called Icy Touch. Frost DKs can also apply the disease using Chains of Ice with the talent Endless Winter, or with their 50-point talent Hungering Cold.
Since a lot of DK abilities scale with the number of diseases, a DKs dps rotation starts with Plague Strike and Icy Touch (or sometimes Chains of Ice in the case of a PVPing frost DK), then moving on to other more hard-hitting abilities. Now, here's a thing to notice. With the exception of Hungering Cold, which in any case costs a lot of runic power, all of their disease-applying abilities cost runes. Translated to a healer: If you remove their diseases, they'll be forced to either reapply the diseases, or use their other abilities without the bonus damage from diseases. In many cases newbie DKs will do the latter, because they don't react fast enough when a disease is removed. That's fine with me, I don't mind they using lots of rune on abilities which nets them far less damage than the optimal. If they choose to reapply the diseases, they're burning runes which they could've used for more hard-hitting abilities, and they may only do it twice before having to wait for runes (barring death runes and the like).
Note that you'll often run into DKs with the talent Virulence, which gives them a bit of defense against disease-removing abilities.
Bottom line; Removing their diseases is worth it. Here's a tip for some shamans and priests: If you don't have it on your hotbars, bind a key to Cure Disease (Shammy or Priestly version) in addition to Disease Cleansing Totem and Abolish Disease. When you first get diseased, use the latter version (which ticks), and then spam Cure Disease on the next disease. Well, at least in the case of priests. For shammies you can argue that it might be better to spam the totem because of the 1 sec gcd rather than 1.5 sec gcd on Cure Disease.
Luckily for us, DKs doesn't have a healing debuff (like Mortal Strike). What they do have is the ability to remove HoTs. Plague Strike, the same ability I discussed earlier, is garantueed to remove a HoT. Further, the disease Blood Plague which it applies has a 25% chance on each tick to remove a HoT.
Does this mean that it's pointless to use HoTs against them?
Not nescessarily. A DK can only use Plague Strike twice before waiting for rune CD, and it provides less damage than other abilities. Thus, it's not garantueed that all your HoTs will be useless. With that said, priests, who only have one HoT, should avoid using Renew, as it's often wasted mana and GCD. Shamans shouldn't worry about Earthliving, as it's essentially free healing anyway. Riptide provides half healing up front anyway, and is often worth casting anyway, since you can do it while moving.
Finally, Druids... DKs are your nemises, right? Actually, it's not so bad. Since you can easily load up 5 HoTs on the same target (Regrowth + Rejuvenation + 3xLifebloom), 6 if you really want to (+ Wild Growth), it's still absolutely worth casting them. A single DK is unable to remove them fast enough.
Edit:Comments on this post from Paendorrah and anonymus poster disagree a bit, but it seems that Plague Strike and Blood Plague ticks remove an entire stack of Lifebloom, rather than just one application. That's bad news for druids, of course. In that case, it's not a good idea to stack up lifebloom. Stick to a single application of Lifebloom for the DKs targets.
Paladins, lacking any HoT, isn't affected at all. It all evens out, somehow.
While DKs have some ranged abilities, most of their damage is from melee abilities. Further, if they can't get into melee, they can't generate a lot of runic power for their signature ranged attack Death Coil. To help them stay in melee, any smart DK will ensnare their opponent. Their only core snare is Chains of Ice, which is rather unique compared to other snares. Note that while you're 100% snared, you're not silenced and can cast anything you want, cast-time or instants. In addition to the snare, a frost DK will also apply Frost Fever with it, with the talent Endless Winter. Further, most Frost DKs and often other specced PVP DKs will have 30 yards range on the snare, thanks to Icy Reach.
So, how to counter Chains of Ice? Moderately easy, actually. Druids can shift ouf of it anyway, priests can Dispel it, paladins can Cleanse it (which also removes a disease, lucky you) or use Hand of Freedom. Shamans... will have to suck it up. Outside of the enhancement talent Earthen Power, there are few ways to get out of it. Sorry.
Also notice that Chains of Ice costs a frost rune, meaning a DK can only apply it twice in a ten sec period. And if they're not frost, that means they can't apply Icy Touch, meaning less incoming damage due to lack of one of their diseases. On the other hand, most DKs will early blow Chains of Ice and Icy Touch, but that means they can't reapply their best snare again very soon.
The other two snares a DK has access to are frost talent Chilblains and the unholy talent Desecration. Chilblains, as I see it, is a PVP talent designed to lightly snare the opponent for a longer duration... as long as Frost Fever lasts, up to 18 seconds with Epidemic. But since druids can shift out of it and all other healers can remove Frost Fever, it doesn't really seem like a giant threat to us healers. The other snare, Desecration, is worse. It seems to work like Frost Trap, which means the only real counter is Hand of Freedom and trying to move out of it.
Outside of running up to their target, a DK has one way of getting into melee with an enemy... by pulling the enemy to himself. Enter the evil chain, Death Grip, a DKs staple tanking and PVP ability. Since it is instant and has 30 yards range, there are few counters to it. The only one I know of is Grounding Totem, and it might just as well swallow their initial Chains of Ice instead, as many DKs open with that instead. But that's not nescessarily a bad thing at all.
Though I said there are no counters, there are still something you should keep in mind. While flying through the air, there's nothing but your own reactions that prevent you from casting instants. And when landing, there's nothing that prevents you from running away, unless the DK snared you first. Your first reaction should be to cast some instant which will benefit you while being pulled, and then run right through them while using more instants.
A few suggestions. Paladins: Cleanse or Hand of Freedom. Priests: Dispel Magic or Power Word: Shield. You might also time a Psychic Scream the moment you land. Don't cast Abolish Disease until you actually have a disease on yourself, and priority on removing snares before diseases (unless you can do both at the same time). Druids: Nature's Grasp, Barkskin or shift to Bear, so you can Enrage and Bash the DK as you land. Shaman: Frost Shock the DK so he has a harder time getting you into melee or use Grounding Totem if it's off cooldown.
The huge danger of Death Grip isn't that you're getting pulled to the DK. It's that you get pulled to the DK and his friends. If that happens, you're probably screwed.
Snares... the other way around
Here's one of the DKs huge weaknessess.... they're very suspectable to snares themselves. They have no inherit ability to break snares, and only Death Grip to get into melee. A good frost mage will screw a DK around any day. Unfortunately, priests and paladins can't exploit that. Druids, on the other hand... ready to get your revenge? Root the sorry buggers. Shamans should keep the DKs perma-snared. Unfortunately, Chains of Ice is a better snare than Frost Shock and Earthbind Totem. However, it is possible to build up enough range so that they have to reapply Chains of Ice, or wait for it to come off cooldown. Toughness and Imp Ghost Wolf help a lot here.
Silence and interrupts
DKs, as the only class I know of, have both a silence and an interrupt at their disposal. Good thing they don't pack a lot of stuns as well. I know only of their pet ghoul stun.
First, their silence. It's called Strangulate and packs a 30 yard range and a 2 min cooldown. Okay, I can live with that. But then there's the Glyph. 20 yards additional range? 50 yards range on a silence? Are you kidding me? I don't know what blizz is thinking here. Earlier, they've reinforced a 30 yard base range on most ranged attacks with talents pushing them to around 36 yards, and a few a very few classes/specs being able to reach a bit above 40 yards. Healing has always been set in stone to 40 yards range. And now DKs can silence u s from 50 yards range? ... No, I don't understand what they're thinking at all. Okay, that was a bit of rant. Until they choose to fix it, we'll have to live with that.
Second, their interrupt. It's called Mind Freeze, and has (fortunately) melee range. Except the cost, it's identical to Pummel. Frost DKs can remove the cost completely thanks to Endless Winter. Notice that without being frost, the cost of 20 runic power means that a DK can't use it from the start of combat, and they need to use no less than two attacks to get enough runic power to use it. Translation: If they've got an empty runic power bar, you don't risk an interruption. You still risk being silenced, but juking/fake-casting won't prevent that anyway.
All DKs have a core ability called Death Strike which will heal them for a serious amount when used. The good news about this one is that they can heal themselves in place of doing a lot more damage with other abilities. Blood DKs have a particular hefty amount of health-restoring abilities.
The important observation: Even if you see a DK on low health, chances are that he can get his health up relatively fast. Unlike a warrior, you can't rely on bursting them down while on low health, but it's still worth trying. Just make sure you keep your priorities in the right order, like trying to stay out of melee. Should they get you in melee, they can restore a lot of health.
Other stuff to know
DKs have a large number of defensive cooldowns. These are the ones to look out for:
- Icebound Fortitude: Core ability. Don't waste stuns while this is up.
- Anti-Magic Shell: Core ability. Prevents any harmful magic effect from landing, and gives the DK additional runic power. Short duration, only 5 sec, so wait for it to fade.
- Anti-Magic Zone: Unholy talent. Major pain for casters. Here's the big thing: It's stationary, so you can just pull the DK with you out of it.
- Bone Shield: Unholy talent. Also improves offense. Dispel or Purge it if you can, otherwise ignore it.
- Lichborne: Frost talent. Don't waste stuns or fears while this is up. Scary how they can chain Icebound Fortitude and this, giving them 27 sec of stun immunity. They're also no longer considered humanoid, meaning Hex won't work on them. But wait! There's light at the end of the tunnel. By activating Lichborne, the DK is considered undead. What does that mean? Good news for a priest or a pally. A priest can then use Shackle Undead on the DK for quality crowd control. For a paladin, some buttons suddenly become usable. Exorcism and Holy Wrath for quality burst damage (sadly, they're immune to the stun) and Turn Evil for crowd control. I haven't confirmed this, but if the DK is feared while Lichborne fades, the fade doesn't automatically break just because they've changed type again. What does this mean? Try to get in a Turn Evil right before it breaks, and watch them run around like chickens.
- Unbreakable Armor: Frost talent. Nothing particular to worry about for healers.
- (Glyphed + Improved) Rune Tap: Blood talent. There's no real way of preventing them from using it.
Unholy DKs, and some off-specced Frost and Blood DKs with the talent Shadow of Death will, when brought to 0 health, automatically rise to unlife as a ghoul for a limited time. There is an important delay from when they die to when they're in control of their character again, during which the DK is immune to all damage. When you see it, run away. The best way to handle such the ghoul is to just outlive it, as it will die on it's own in a bit. They can still pack a good amount of damage, but seem to loose all their snares and Death Grip. If you're a priest, Shackle it. If they've got a pet ghoul, it will still be active until they die for good.
All DKs have the ability to Raise Dead. For non-Unholy DKs, this will give them a guardian for a limited time which they can't directly control. On the other hand, Unholy DKs with the talent Master of Ghouls will gain a pet without duration, which they can control for additional fun. At least for them. They also gain additional abilities, namely Leap (which means it's hard not to have this guy on top of you all the time), Huddle (which means that it's very hard to focus-kill the ghoul pet of a smart DK) and Gnaw (a DKs only stun).
The ghoul does a non-trivial amount of dps on their own. What to do about the pet? If you're a priest, Shackle it (unless the master is a zombie as well, in which case he makes a better shackle target). Also try to catch both when you Psychic Scream. If you're a druid, you can treat it the same way as a hunter pet, except that you can't hibernate it. If you're a shammy, you can (in BGs, not in arenas) use Earth Elemenetal totem to get him out of your face, but at the expense of other earth totems. Otherwise, you can try to Earthbind both the DK and the ghoul. If you're a pally, you may use Holy Wrath and Exorcism to try to burn it down, or Turn Evil for crowd control. However, the first two mentioned abilities have cooldowns, and it might be very handy to save those cooldowns in case the DK should activate Lichborne (see above). While Turn Evil doesn't have a cooldown, you need to weigh up the result against the risk that you eat a Mind Freeze, rendering all your spells unavailable for 4 sec. Apart from the ghoul stun, the pet is less of a treat against pallies with their high armor.
Mark of Blood
A blood talent which is worth worrying about. It's not dangerous to ourselves as we rarely melee enemies, but it can really be dangerous if they use it on your arena partner. Remove it if you can, otherwise try to convince your ally to hold back for a bit and mitigate damage until the mark runs out.
There are two abilities whose duration depend on how much Runic Power the DK has/can generate, namely the blood talent Dancing Rune Weapon and the unholy talent Summon Gargoyle. These two abilities can last for a really long time if the DK can keep generating runic power. They vanish as soon as the DK run out of it.
Apart from the pet stun, a DKs only CC is the frost 51-point talent Hungering Cold. It requires a lot of runic power, but has no inheret cooldown. Try to avoid being caught with your arena partner.
And that's all, folks. Hope you've learned something. I'll probably learn more myself too, in which case I might update the guide.
Edit: Thanks to all commenters, I've added edited the post with the clarifications you've shared with me.