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Feng the Accursed
Feng the Accursed is the second raid boss of the Mogu'shan Vaults raid instance. The encounter is divided into three phases, during which the boss uses a variety of different abilities.
While the encounter is not a difficult one, it will place considerably strain on your healer, and it requires very good execution from the rest of your raid.
Overview of the Fight
The encounter against Feng the Accursed is a three-phase fight.
- Between 100% and 95% health, the boss simply melees and deals a minor amount of raid damage through an ability that he uses throughout the fight (one of the shared abilities we discuss below).
- Phase One begins at 95% health and ends at 66% health.
- Phase Two begins at 66% health and ends at 33% heath.
- Phase Three begins at 33% health and ends when the boss is dead.
During each phase, the boss uses 2 abilities specific to that phase. He also has two shared abilities, which he uses during all phases. One of the two shared abilities (a stacking debuff applied to the tank) changes slightly in each phase, but we will still treat it as a single ability.
The fight is exclusively single-target; there are no adds or secondary targets to attack.
The fight presents a small peculiarity, in that the tanks gain access to two abilities that can be used to help the raid deal with some of the encounter mechanics. We explain these abilities in the section directly below this one.
Helpful Abilities
In order to help your raid deal with some of the mechanics, your tanks gain access to two abilities, which take the form of a special action button. The abilities are not given to the tanks by default; there are two small objects present on the ground, at the start of the fight. Clicking these objects will grant the clicking tank the respective ability.
There are only two crystals, one for each of the two abilities, and each tank can only have one ability.
The abilities are:
Nullification Barrier creates a sizeable protective barrier around the tank who uses it, lasting up to 6 seconds (it is channeled). Anyone inside the barrier is protected from magic damage and debuffs. The ability has a 1-minute cooldown. It is interesting to note that this spell also affects the boss, preventing him from receiving certain buffs from his own abilities.
Shroud of Reversal is a buff that the tank can place on a raid member. This allows the tank to mimic the first spell cast against that ally, and to cast it back at the boss. The ability has a 30-second cooldown.
Shroud of Reversal appears to play a much less important role in your raid's success than Nullification Barrier. It is mostly useful for obtaining the achievement associated with this encounter, as we explain in our achievement section. Outside of this, it is only useful for dealing a bit of extra damage to the boss. We were unable to test Shroud of Reversal properly on the Beta, and we will update the guide as soon as we know more.
This guide will assume that both of these abilities have been taken by your tanks.
Shared Abilities
Regardless of the phase he is in, Feng the Accursed regularly casts 
Spirit Bolt, dealing Shadow damage to random raid members. The frequency of this spell is rather high, but it varies depending on when Feng casts his other abilities.
Moreover, in each phase, Feng applies a stacking debuff to the tanks, which requires a tank switch. The debuffs, by phase, are:
Lightning Lash is a stacking debuff that Feng applies to the tank. It deals Nature damage every 2 seconds for 20 seconds.
Flaming Spear is a stacking debuff that Feng applies to the tank. It deals Fire damage every 2 seconds for 20 seconds.
Arcane Shock is a stacking debuff that Feng applies to the tank. It deals Arcane damage every 2 seconds for 20 seconds.
These abilities all warrant a tank switch. We recommend that the off-tank taunts the boss when the current tank has 2 stacks of the debuff. Also, it seems that Shroud of Reversal can be successfully used to mimic these debuffs, and apply them to the boss.
Phase One: Spirit of the Fist
Phase One begins when Feng reaches 95% health. Between 100% and 95% health, the boss will simply melee and cast Spirit Bolt. At 95% health, the boss will travel to the statue of the Spirit of the Fist, and imbue himself with the abilities of this spirit.
The phase ends when the boss reaches 66% health, at which point he enters Phase Two.
Abilities
During Phase One, Feng makes regular use of 2 abilities, in addition to the shared ones mentioned at the start of the guide.
Epicenter is an earthquake that lasts for 10 seconds and deals damage to all raid members every second. The damage of Epicenter is lower, the farther from the boss you are while he is channeling the spell. Additionally, while Epicenter is being channeled, all players are debuffed with a 75% reduced chance to hit. Feng casts Epicenter once every 30 seconds.
Lightning Fists is a harmful spell, essentially a shockwave, that travels along the ground. Anyone in the path of the shockwave takes a large amount of Nature damage, and is stunned for 5 seconds.
Strategy
Positioning
As mentioned above, at the start of the phase, Feng moves to the statue of the Spirit of the Fist. There is no reason to move him from this location, so this section will assume that he is tanked there.
Melee DPS players and tanks will, of course, be in melee range. Ranged DPS players and healers should spread out loosely around the center of the room.
When the boss casts Epicenter, all melee and ranged raid members must stack in the center of the room.
Epicenter
The main issue in Phase One is dealing with Epicenter. Dealing with this ability is made considerably easier thanks by Nullification Barrier.
As we mentioned above, each time Epicenter is cast, the raid should stack in the center of the room, and alternate healing and defensive cooldowns to survive the damage. Since Epicenter is cast every 30 seconds, the tank who has Nullification Barrier can cover every other Epicenter. For the remaining ones, the healers will have to come up with a rotation of defensive abilities.
When Epicenter is not covered by Nullification Barrier, all ranged DPS players will have to deal with the 75% reduced chance to hit. While this is unavoidable, players should look for ways to minimise the effect this has on their DPS. For example, DoT classes should refresh the DoTs before the Epicenter starts, so that they continue to tick throughout its duration.
Lightning Fists
Lightning Fists is not at all difficult to deal with. Each individual raid member must pay attention to the visual effect of the ability (a sort of lightning that travels along the floor) and avoid being hit by it.
Phase Two: Spirit of the Spear
Phase Two begins when the boss reaches 66% health. The boss will travel to the statue of the Spirit of the Spear, and imbue himself with the abilities of this spirit.
The phase ends when the boss reaches 33% health, at which point he enters Phase Three.
Abilities
During Phase Two, Feng makes use of 2 abilities, in addition to the shared ones mentioned at the start of the guide.
Wildfire Spark is a debuff placed on a random raid member, which, after 5 seconds, turns into a fire patch. The fire patch expands and moves along the floor of the room, dealing high Fire damage per second to anyone standing in it. Feng applies this debuff 5 times in quick succession to 5 random raid members, after which he pauses for about 30 seconds, before applying it 5 times again, and so on. During his pauses, he uses Draw Flame, his other ability, which we explain below.- Draw Flame is an ability that Feng uses to absorb all the wildfire present in the room, stacking a buff on himself. The number of stacks of the buff is proportional to the amount of wildfire that he absorbs. The buff causes Feng's melee swings to deal a large amount of Fire damage to the entire raid. Each melee swing removes a stack of the buff. Feng casts this ability every 30 seconds. Entering Phase Three does not remove Feng's Draw Flame buff, if it is active.
Strategy
Wildfire Spark
Wildfire spreads whenever players come in contact with it. This should be avoided, since more patches of wildfire result in more raid damage dealt by the boss due to Draw Flame.
Whenever a player is affected by the Wildfire Spark debuff, they should be quick to move away from other raid members, preferably to an unoccupied edge of the room.
It is important to note that the wildfire patches travel slowly along the floor, so players must always be aware of their position and check if any wildfires are approaching.
Draw Flame
Draw Flame will result in a large amount of raid damage, even if your raid has controlled the wildfire patches perfectly. This will require a large amount of healing, as well as healing and defensive cooldowns.
Nullification Barrier, if cast on the boss when Draw Flame is about to finish casting, will prevent Feng from applying the buff from Draw Flame, effectively negating the ability. This is possible every other Draw Flame cast.
For the remaining casts, the raid will have to stack up in order for healing to be made possible, which will cause problems with wildfire patches, but this is something that is unavoidable. Your raid must simply be quick to reposition in case a wildfire patch approaches.
Tanks should be prepared to use any abilities they have to get away from the boss and kite for a few seconds. These abilities should be saved for when the raid is in critical condition, to give healers a few extra seconds to recover.
As we mentioned above, the Draw Flame buff is carried over into Phase Three, should the boss be pushed to 33% health while the buff is active. This will result in increased raid damage during Phase Three, which, as you will see, also contains a fair amount of raid damage.
While it is possible to heal through this damage, your raid might find it better to delay pushing Feng to 33% health until a time when his Draw Flame buff is not up.
Phase Three: Spirit of the Staff
Phase Three begins when the boss reaches 33% health. The boss will travel to the statue of the Spirit of the Staff, and imbue himself with the abilities of this spirit.
The phase ends when Feng the Accursed dies.
Abilities
During Phase Three, Feng makes use of 2 abilities, in addition to the shared ones mentioned at the start of the guide.
- Arcane Velocity is a channeled spell that deals raid-wide damage to all players. The farther players are from the boss, the more damage they take. Feng casts this ability roughly every 20 seconds.
Arcane Resonance is a debuff placed on a random raid member. This debuff causes Arcane damage every second to that player and to all allies within 6 yards. The damage done to allies is increased for each player affected. This debuff is cast roughly every 20 seconds.
Strategy
Because of the way in which Arcane Velocity deals its damage, your entire raid should be close to the boss. Whenever Arcane Velocity is cast, everyone should stack up on the boss. This will not only reduce the damage done by Arcane Velocity, but also make healing easier.
You cannot, however, remain stacked, due to Arcane Resonance. When this debuff is cast, there is very little time for the affected player(s) before the damage they deal to nearby raid members is deadly. Feng cannot cast Arcane Resonance while he is channeling Arcane Velocity, but if Arcane Velocity is off cooldown, he will cast it immediately after the channel is over. As such, your raid should spread out around Feng again, about 2 seconds before the Arcane Velocity cast ends.
Similarly, in order to minimise the risk of Arcane Resonance hitting players, your raid should only move in next to Feng right as he starts his Arcane Velocity cast, and not before.
Outside of these two considerations, this phase is a "final burn" sort of phase, where both healing and DPS cooldowns should be used.
When to Use Heroism/Bloodlust/Time Warp
We recommend using 
Heroism/
Bloodlust/
Time Warp during Phase Three. There are two reasons for this. Firstly, this is because during this phase, raid movement is at a minimum. Secondly, it is because this phase is the most intense one, and you want to get it over with as quickly as possible.
Learning the Fight
Due to the sequential nature of the encounter's phases, your raid will have to progresses through Phase One in order to learn Phase Two, and again through both Phases One and Two in order to learn Phase Three. Therefore, this dictates a rather clear learning path.
We recommend that you focus on your raid understanding and learning to execute each phase properly, because simply blundering or zerging your way past Phase One or Two will not give you the required amount of calmness required to get through Phase Three.
Achievement: Anything You Can Do, I Can Do Better...
The 
Anything You Can Do, I Can Do Better... achievement is part of the 
Glory of the Pandaria Raider meta achievement. The achievement requires that Shroud of Reversal be used to mimic all of the following abilities:
As you can tell, the success of the achievement is left up to your raid's tanks (the only ones who can use Shroud of Reversal). It is a matter of simply casting Shroud of Reversal on:
- a player who is near the boss when he casts Epicenter;
- a player who will intentionally stand in the path of Lightning Fists;
- a player who is afflicted by the Wildfire Spark debuff;
- a player who will take damage from Arcane Velocity;
- a player who is afflicted by the Arcane Resonance debuff.
Fortunately, the achievement can be completed over the course of successive attempts (and/or kills), each element of it being counted separately and regardless of the outcome of the encounter.
(information from Icy Veins)