There are a number of reasons why raids would want to use warlocks as tanks:
Ability to gain and maintain aggro at range:
this is the primary reason why we're asked to tank. Generally these encounters involve bosses with some form of ranged magic-based attack. They also usually have some nasty ability that makes traditional melee tanking difficult or even impossible. With well-timed Curses of Doom to gain snap aggro, and Searing Pain
to hold the bosses' attention, warlocks can generate enough threat from a distance to allow other DPSers to do their job.
a 5/5 Master Demonologist
has access to one of the best sources of resistance: the Felhunter. Having a felhound around increases all resistances of both pet and master by 70. This buff is stackable with the resistance auras of paladins and shamans, and resistances from consumables and gear. In other words, warlocks probably have the easiest time hitting the resist cap of 365, thereby mitigating as much damage as possible from a specific school of magic.
Survivability: Warlock gear, in general, come weighted with Stamina - a tank requisite. Warlocks also have access to a variety of self-heals: drain life, siphon life and even deathcoil, to a smaller extent. Most importantly, Soul Link provides a healthy buffer for the tanking lock, as long as the pet is healed at the same time. The synergy between Master Demonologist and Soul Link makes Demonology the ideal "resistance tanking" tree. Access to healthstones and soulstones definitely helps as well.
Who is Leo?
Leotheras the Blind is probably the first tanking assignment for many raiding warlocks in The Burning Crusade. Lore-wise, he could be one of the two blood elves who survived Illidan's demon hunter training (the other being Varedis). Unfortunately, Leo spent too much time collecting gloves - or glove tokens, to be specific - and didn't come out at the top of the class.
He still has trouble containing his inner demon (although he has absolutely no issues with drawing the bad mojo out of others). As a result of this inadequacy as a demon hunter, he's been relegated to his hole under the water, and spends his days waiting for 25-man raiding parties to rob him of his Tier 5 glove (token) collection.
On the other hand, Varedis, the star student, has the more glamorous job of training more demon hunters at the Ruins of Karabor, just outside his master's crib at the Black Temple. Unfortunately, he is rendered a weakling by the Book of Fel Names, and can be easily disposed of by a 5-man, or even a 4-man, team. Moral of the story with Leotheras and Varedis: you can be a raid boss even if you didn't do well in school.
Gearing up for Leo
A single Warlock tanks Leotheras when he switches into his demon form. In this form, Leo launches a Chaos Blast bolt that splashes in a circle every two seconds or so, creating a stackable 45-second debuff that increases fire damage taken by 1,675. The splash is centered on Leo's target, so it will do well for the rest of the raid to stay away from the toon tanking* demon Leo. The gearing strategy of the Warlock tank is centered on three stats: Fire Resistance, Stamina and Spell Hit.
Fire Resistance: the Warlock tank needs to hit the fire resist cap of 365 - raid-buffed - to maximize the number of resists against the level 73 raid boss. It's easy to stack fire resistance to a level way more than 365, but additional points above the cap do not contribute anything more to damage mitigation. So don't go crazy stacking fire resist at the expense of two other critical stats for this role: Stamina and Spell Hit.
it's simple - get as much of Stamina as possible, without compromising spell hit. The Warlock tank will suffer very spiky damage in this encounter due to the binary nature
of the Chaos Blast attack. With a fire resist of 365, the Warlock will take neither damage nor debuff 75% of the time, but full damage and debuff
in the other 25%. Leo's demon form lasts for about 60 seconds. Given that Chaos Blast is cast every two seconds and a 75% resist rate, the tanking warlock will have about seven debuffs near the end of the phase. At seven debuffs, an unresisted Chaos Blast will hit for close to 12,000 fire damage! This means that the warlock tank must
have 12,000 health at the bare minimum; a raid-buffed health of 14-15k is recommended. Soul Link will really help here, by having your pet wick away 20% of that damage. Healers in the raid must also take note of keeping the Warlock's pet alive, since he or she is relying on it for soaking damage and
It bears repeating here again that having a spell hit of 202
will minimize the chances of level 73 bosses dodging your spells. In this encounter, missed spells might mean losing raid DPS as a whole during his demon form phase, since you are generating less threat. While a hit cap isn't essential, it is important not to compromise this stat too much while you are loading up on fire resistance and stamina.
This list includes the best fire resist gear currently available and should be a good starting point for warlocks gearing up to tank Leo. The following fire resistance buffs should be taken into consideration while planning your gear:
This accounts for 175 fire resist, which means that your gear only needs to contribute 190 to hit the resist cap of 365. Some additional resistance doesn't hurt really; it'll come in handy if your paladin is taken down during the fight, for example. Other consumables that help with the encounter include the Major Fire Protection Potion, which will help take some spikiness away from the fire damage.
For new Warlock tanks (or locks with less Stamina gear), Soul Link significantly increases the margin of error allowable for this fight. It also gives your healers more room to breathe, although it means that they have to take care of your pet as well. This is an example of a Leo tanking build, that hits Master Demonologist for fire resist, Soul Link for survivability and some destruction talents for DPS and threat generation:
Fighting the good fight
Leotheras alternates between his two forms for much of the encounter. He starts with his elf form which lasts close to a minute in the beginning of the encounter. Land a Curse of Doom as soon as Leo is free, so that it will pop just after he assumes his demon form to gain some quick snap aggro.
The demon form lasts for 60 seconds, during which you'll be pretty much spamming searing pain, popping consumables and crying for heals on voice. About 14 seconds before he switches back to his 45-second elf form, you want to land another Curse of Doom. The objective is again to make sure that CoD pops when he goes back to demon form in the next phase.
The tanking period will be the longest in the final phase, when Leo hits 15% life. This is where his bad side (not that he has a good side) totally goes out of control and becomes a separate entity. The raid now has to contend with both elf Leo and demon Leo at the same time. Many warlocks succumb at this stage due to simply having too many stacked debuffs. If you die, don't panic, pop your soulstone, insta-summon your felhunter (not forgeting to repostion it out of harm's way), reacquire aggro with searing pain and use all available means to stay alive. Have other warlocks in your raid ready to chain their soulstones on you if needed. A warlock tank keeps coming back for more!
There we have it, a Warlock's perspective of tanking Leotheras the Blind. Full raid guides are fairly easily available elsewhere, or if you prefer, these illustrated guides are a good - and entertaining - alternative. The hilarious but strictly adult-oriented "How not to suck on Leo" guide can be found here.
* Some guilds have successfully used a fire resist Druid or Warrior tank for this phase since the nerfing of the Chaos Blast AoE, and melee DPSers have been able to hit Leo at the extremities of his hit box and not be affected by the debuff. However, rage generation has been reported to be an issue due to resists, leading to a lower raid DPS in the demon phase.
Note: In my previous article, I made the erroneous assumption that the specs reflected in the Armory were the same specs used when the WWS Scoreboard was compiled. The scoreboard relies on past WWS data and the warlocks in question may have already changed their specs in the meantime. Thus my conjecture that 0/21/40 isn't the "standard" build at those levels is flawed - I apologize and thank you, Ryan, for pointing this out. This strengthens the case for 0/21/40 being the highest DPS build, and the cookie-cutter build for many high-end encounters unfortunately.
V'Ming still spends his time laughing ominously, but in the hallways of Tempest Keep and depths of Serpentshrine Caverns now.