There are actually alternatives to the regular tanking classes, warrior, dk, druid and paladin. In some parts of the game, most of the other classes work well, or are even needed, to tank something. In fact most classes have successfully tanked some end-game material. Maybe not always raid bosses, as some rogues have managed to do, but in any case some heroics. And for some raids you even need a mage (Gruuls Lair), warlock (SSC) or hunter (UBRS) to tank some part of a boss encounter in various ways.
But for this post I thought I'd look more into where the alternatives not only work as freak exceptions, but as really viable options. The LFG-tool has hindered this to some part (or nearly entirely actually) since you can't choose to join as a tank unless you count as one of the regular tank classes. This means if you ever want to tank when being an alternative class, you have to hope for either a tank that doesn't mind sharing the tanking business with you, or a tank that isn't there (i.e stepping in for a tank that has left/afked). Or collect a bunch of lowbie friends on your own server of course.
If you play the game for the very first time you'll have plenty of new stuff to keep you entertained in any case, and maybe this isn't something for you. But aiming to become a viable tank-alternative could be an interesting way to level that fifty-eleventh alt. So if you like a new take to the game, this might be something for you.
Just to clarify, the real tank classes are there for a reason of course. No matter how well you gear for it, there will be alot of content you simply can't tank for various reasons, most of it being closer to the end-game, because that is when the mobs start hitting too hard. Just so you don't get your hopes up for being able to warlock/hunter/shaman/etc tank ICC eventually. That won't happen.
Alternative tanking is highly affected on changes that are constantly made to a class. This means you can have a warlock tank Sarth 3d or a mage tank Razuvious one day (it has happened), and not the other day, simply because of the changes done to the class. Since the class isn't supposed to tank in the first place, Blizzard won't have much regard to their tankability when they apply changes to these classes.
Tankability: approximately level 10-60ish
There are some features that make warlock a decent alternative to a "real" tank.
- First of all, they have a pet (voidwalker, alternatively felguard later on) which actually has stats as a real tank. Lots of armor and hp. The drawback of using a pet instead of a regular tank is that it's a little trickier. It requires the rest of the group to mind their threat a lot more, as a pet doesn't respond as well to new situations than a player tank can. There are alot of really sucky tanks out there however, who don't know their taunt from a banana, and compared to them I'd even say a pet tank is -better-. I say the group have to mind their threat because a Voidwalker and Felguard don't have a taunt in the real sense. That means if the pet looses aggro, he'll have a hell of a time getting it back. The skills they have simply increase their own threat, but it doesn't snatch it back from someone else, which is a significant difference.
- Secondly, the voidwalker allows the warlock itself to take a pounding. Recent buffs to the Voidwalkers Sacrifice skill allows the warlock to get a really good shield, without having to actually sacrifice the pet (which was previously the case). It removes a small amount of hp from your Voidwalker, but the ratio is really good. I don't know the exact numbers, and it differs depending on level and skill level of course, but I'd guess it's something like 1:10. That means that 100hp sacrificed from your pet gives you a shield that soaks 1000 dmg. Not bad at all. You get this skill at level 16.
- Thirdly, the talent Improved Healthfunnel in the demo tree allows your pet to regain hp and take 30% less dmg when channeled. That's alot of damage reduce, and a great way to let the pet tank hard hitting elites successfully. It was by using this talent some warlock managed to tank Sartharion 3d. While he just channeled health funnel, everyone else went bananas with dmg on the boss, using Miss Direction and the like to keep threat on the pet. Something you can't count on happening when on low levels however.
- Forthly, warlocks actually have a skill which causes a high amount of threat in Searing Pain. This means you can keep aggro on yourself at least, if necessary, eventhough you can't move this threat to your pet unfortunately.
There are two viable specs for the aspiring warlock tank. Either you put all your cards on your pet being the tank through a demonology spec, or you set out to tank stuff yourself with an affliction spec. Both have their pros and cons of course.
Demonology Pet-tank: The pet will tank through high hp and foremost high armor, something the warlock will never be able to get (except for with metamorphosis). Through a demonology spec you improve the pets stats and threatability. You will also get Metamorphosis at level 50 which allows the warlock to enter a sort of "tank mode" where they get alot higher armor and a real taunt. This buff is only up for some 30 seconds and has a 3 minute cooldown. This can be changed with some glyphs and talents, but there will still be a gap where you can't be in this form. This is where you have to use your pet instead. This spec works best against single-target hard hitting mobs, such as bosses.
Affliction Warlock-tank: A warlock can tank through huge hp-gains, which compensate for not having alot of armor. When having an affliction spec and alot of targets to use their dots on they will regain alot of hp. Combining this with the Voidwalker shield and a high hp-pool they can take quite the beating. However, being a clothie, the warlock will take big hits, and they can't fight anything that risks one-shotting them through a crit. Also if the warlock only has one target, like say a boss, the hp-gain might not be high enough to compensate for the hp-loss. Therefore an affliction spec works best against larger packs of mobs that don't hit too hard, like trash in an instance.
Important to remember is that the pet benefits from the stats of the warlock. As a tank warlock there is one really important stat to collect, whether you are demonologist or afflictionist - stamina. Also spellpower will help you with the hp-gain if you're an affliction lock. To my knowledge there is no cloth gear with defense stats on them, so there is no point in trying to be crit-immune. Like an old-school druid you have to soak the damage with big amounts of hp instead and work it so that the health you gain is bigger than the health you lose.