This is the rumored Faction Champions AI Threat Mechanics.    Just ripping it and posting below for people to see.

Gist of it, Proximity, Armor, Resistance and High HP is what will keep them from attacking you.   Can use Resistance Flasks, Armor Pots to "reduce your threat".    If you want "tanks" in this fight to hold aggro, never heal them to full, keep everyone else full, let tanks be the lower HP target.   Also, their healers operate on pumping full heals into lowest hp target, so when our kill target gets low, that's the best time to start CC'ing healers.

http://maintankadin.failsafedesign.com/forum/index.php?rb_v=viewtopic&f=...

General Concepts

The first important point to understand about
faction champions is that nothing is random, as much as it may seem so
upon first learning the fight. Every action the mobs take is governed
by very specific rules, all of which may be controlled to your favor by
understanding the priority system behind their AI.

The most
important principle to understand is that all the Faction Champions are
governed by threat. It is often said that they have no threat table,
but this is a myth. You can even see their threat table on omen when
you target one of the mobs.

How is this testable?
Look
at omen while targeting a Faction Champion. Observe the fact that
threat drop abilities such as Feign Death or Fade work as normal on
Faction Champions, even on Heroic Difficulty. Observe the fact that
taunt effects function as normal on Normal Difficulty, indicating that
threat rules exist and can be manipulated using the normal tools, even
if they function according to unusual rules.

The cause of
the misunderstanding that Faction Champions have no threat is the fact
that their threat is not the result of damage taken or healing sensed.
It is calculated by different rules than any other encounter in the
game.

These are those rules.

~~~~~~~~~~~~~~~~~~~~~~~~~

Melee DPS Champions

Melee
DPS Faction Champions calculate their threat based on an additive
combination of 3 factors. Each of the three appear to share equal
priority for determining target, and the threat list constantly updates.
These factors are ARMOR, PROXIMITY, and HEALTH DEFICIT.

ARMOR
Armor
is the first factor of targeting priority and refers to the exact armor
value displayed on your character tab. The lower the absolute value of
armor on a potential target, the higher the threat.
LOWER ARMOR = HIGHER THREAT

How is this testable?
Have
two warlocks stand exactly on top of each other. Have them both
activate the spell Fel Armor. Warlocks are one of the highest priority
targets in general for Melee when all other factors are equal because
they have one of the lowest relative armor values. At some point, one
of the melee will be almost guaranteed to target and attempt to attack
one of the warlocks wearing Fel Armor. When that happens, have the
warlock who was targeted activate Demon Armor, which grants greatly
increased additional armor value. Unless outside factors interfere, the
melee DPS Faction Champion should always immediately switch targets to
the other lock standing in the same spot as the first one, due to the
lower armor value.

How does this knowledge help me?
Depending
on the class, the understanding of Armor Value's contribution to the
aggro calculation can be exploited in various ways. One of the most
universal is the ability to have your more vulnerable raid members
pre-pot an Indestructible Potion right before entering combat, granting
them an additional 2500 armor and thus a much lower threat signature.
Similarly, a player who finds themselves vulnerable and unable to
escape a melee DPS attacking them may re-actively use an Indestructible
Potion to help them drop threat.
Tanks attempting to pick up a
target or hold it may wish to put on DPS gear or remove their shield.
Players with access to some form of Armor increasing effect such as
Inner Fire should pay particular attention to keeping it active at full
strength unless they wish to deliberately cause Faction Champions to
attack them. Another example is a druid shape-shifting into a higher
armor form if focused, such as a feral druid shifting from cat to bear.
Warlocks are the class most frequently focus-fired by melee DPS Faction
Champions, and their primary threat-signature tool, Demon Armor, was
mentioned in the example above.


PROXIMITY
The
second piece to the melee DPS Faction Champion threat calculation is
proximity; the distance from the Faction Champion to the player. The
shorter the distance, the higher the threat.
CLOSER PROXIMITY = HIGHER THREAT

How is this testable?
Have
a deathknight Death Grip a melee DPS Faction Champion far away from
everyone else in the raid. Then Stun or otherwise CC that Faction
Champion. Have any player stand right next to the CC'd Faction
Champion, and have everyone else move far, far away. Unless significant
outside factors interfere, the Faction Champions will always attempt to
attack the player right next to them. For testing purposes, use a class
with fairly low relative armor to ensure that the armor and health
deficit threat signature of someone else does not override the testing
player's proximity threat signature.

How does this knowledge help me?
It
doesn't really, since the proper way of handling this knowledge is
intuitive already. Melee DPS Faction Champions can only attack you from
melee range, and thus it is natural to want to move away from them if
they are attacking you. This applies to melee DPS attacking the faction
champion too though. It is good practice for a melee DPS who is
targeted by a Faction Champion they are DPSing to run away from the
Faction Champion and cause it to target switch or to be ineffective at
causing any damage until someone else's proximity threat signature
overrides theirs and they begin attempting to attack someone else.
Reducing as much damage taken by the raid as possible is a primary
focus of the entire raid, as the less damage that goes out, the more
the healers can focus on dispelling, which results in a far more stable
control over the encounter. It is also advisable to keep various forms
of snares and movement inhibiting debuffs on melee DPS Faction
Champions as often as possible.


HEALTH DEFICIT
The
third and final component of a player's threat signature for a melee
DPS Faction Champion is their health deficit. This is defined in terms
of the absolute value of hp that player is below their maximum hp. This
is the factor which causes the seemingly random "insta-gibs" where
multiple Faction Champions all target the same player at once and
deliver a devastating combination of attacks. This generally occurs
when someone takes a DoT tick or a low armor value player is clipped by
an aoe effect like Bladestorm. It gives the illusion of intelligence by
causing them to attempt to target whoever is weakest in your raid.
HIGHER HEALTH DEFICIT (more damage taken) = HIGHER THREAT

How is this testable?
Have
a deathknight Death Grip a melee DPS Faction Champion far away from the
rest of the raid. Then Stun it or otherwise CC it. Have two warlocks or
roughly equal armor value stand directly on top of the CC'd Faction
Champion. Have one of them Life Tap to half health or lower to create a
great enough health deficit threat signature to override any minor
differences in armor value threat signature between the two warlocks.
When the Faction Champion comes out of CC, unless outside factors
interfere it will always attempt to attack the warlock at lower health
due to the health deficit from Life Tapping.

How does this knowledge help me?
The
biggest application of this aspect of the threat signature is focusing
a large amount of attention to defensively dispelling DoT and Debuff
effects from your raid. The better your raid's dispelling, the more
controllable the fight will be because there will be no random health
deficits all over the place causing unpredictable target switching to
occur. DoTs tick for hard enough to be a significant danger to raid
members by setting them up for an insta-gib situation where their
health deficit threat signature causes multiple Faction Champions to
all switch targets to them at once.
The other aspect of this
knowledge that can be exploited is that if you are a tank attempting to
control a mob, and you can get a melee DPS Faction Champion far enough
away from the rest of the raid that you have a proximity threat
signature advantage to compensate for your lower armor value threat
signature, if the Faction Champion starts attacking you it will tend to
remain attacking you because it will be constantly causing a health
deficit on you unless outside factors interfere.
Another
application of this applies to warlocks, who should be encouraged to
not Life Tap unless positioned a significant distance away from
dangerous Faction Champions or receiving immediate healing.


SUMMARY

ARMOR VALUE + PROXIMITY + HEALTH DEFICIT = THREAT SIGNATURE

Note:
The rules for melee DPS Faction Champions all also apply to the Hunter
and both the Hunter pet and the Warlock pet. Both pets are subject to
taunt even in Heroic Difficulty.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Ranged DPS Faction Champions

Ranged
DPS Faction Champions function on very similar lines to melee DPS
Faction Champions, with one difference. Instead of Armor Value being
part of their threat calculation, they instead compare Resistance to
their school of magic.

RESISTANCE + PROXIMITY + HEALTH DEFICIT = THREAT

RESISTANCE
This
aspect of the threat calculation is much less noticeable than the armor
value part for melee DPS, since resistance levels tend to be the same
for everyone in the raid due to raid wide buffs like Mark of the Wild,
Auras, and Totems. Some classes have abilities which grant them higher
resistance to magic than normal, and will thus tend to not be targeted
by the caster Faction Champions, but in general casters will simply
deliver killing blow insta-gibs to raid members already being attacked
by melee Faction Champions as health deficit is the primary determining
factor in their targeting.

How is this testable?
Stun
or otherwise CC a caster Faction Champion. Quickly move the entire raid
to the complete opposite side of the room so that they will be out of
range of that Faction Champion's attacks. Have two players, one buffed
with Mark of the Wild, one without Mark of the Wild, stand directly on
top of the CC'ed Faction Champion. When the Faction Champion comes out
of CC, unless outside factors interfere, they should always attack the
player without Mark of the Wild.

How does this knowledge help me?
If
you have players which you find are vulnerable to being focused down by
casters, have them use a Flask of Lesser Resistance (+50 all resists),
which should help significantly to prevent caster Faction Champions
from targeting them unless they have a significant proximity and health
deficit threat signature.


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Healers

Healers
heal based on a very easily recognizable principle. They place priority
on their healing targets based on the lowest absolute hp among friendly
targets. What this means is that out of all Faction Champions with a
health deficit, no matter how big, the one with the lowest numerical
amount of health will be selected as the target of their healing. This
is why it is relatively easy to burn down high health targets at first,
but when they reach lower health all enemy healers will pour massive
amounts of healing into the target and it will be much more difficult
to finish off.

How is this testable?
Have
one player spend the entire fight DPSing the hunter or warlock pet.
Since the pets have much lower absolute health than any of the actual
Faction Champions, as long as the one player is constantly doing damage
to the pet the healers will focus their primary attention on spamming
the pet with healing and HoTs. An enhancement shaman is ideal for this
as they can purge off the HoTs. Observe the healing received meters
following the engagement.

How does this knowledge help me?
Save
your CC diminishing returns on enemy healers for when your kill target
is reaching lower levels of health, and then chain them in sequence to
solidify a kill. As in the method of testing, assign one player, or
alternatively all your raid's pets, to constantly DPS the enemy pets.
Be sure not to kill them. All heals directed at these pets your
interrupters can simply let go through, and save their shocks and kicks
for any heals directed at non-pets. This allows you to do a much more
effective job at eliminating healing onto your kill target.

LOWER ABSOLUTE HEALTH = HIGHER HEALING PRIORITY

Sweet, this has now becomes the Most All Timed viewed page on this site!   And the only page that's not completely outdated and still relavent!

Not sure if this is true or not but I did notice when Lava Crab did 10man Hard mode on these guys i think they each gain another spell(or I just didin't notice it before)

Druid(resto): Nourish

Mage:Arcane Barrage

Warlock: Searing Pain

Priest(Disc): Renew (not realy sure about this one as it's instant cast)

Rogue & Shammy(Enhancement) I'm not sure of as i see no cast bars I'll have a look at parses & see

Looking over logs i saw searing pain in both, so maybe they just get smarter about being locked out(casting it cause i kicked fear & such) also i see wowhead has CoEx listed so the extra ability my still be true

*Fourth

Some observations, having done this fight 3 times this week in 10 man, and twice in 25 man.

10 man seems to be a much tighter fight than 25 man in terms of group comp, and CC's - so it seems like what works for 10 man should certainly work for 25 man.

In 10 man, what worked best was the following:

A) CC rotations - two people (for ex mage and a warlock) cover two CC targets (for ex priest and rogue). Mage starts out by polying priest and warlock starts out fearing rogue. After two applications, the two switch. This CC rotation can be repeated the duration of the fight - as long as no one dies.

B) Kill targets - while a couple of the groups I was in tried killing both healers first...what  ended up going smoothest was killing one healer (pref druid), then killing off the biggest DPS threat (pref rogue), and then proceeding to kill remaining healers. That took a lot of defensive pressure off the team and allowed us to CC / Kill without looking behind our back as much.

C) Raid Killers - the following abilities were absolute raid killers: Warlock Hellfire, Shaman Totems not being stomped, Rogue going unchecked on people (usually clothies), Warrior Bladestorm, and people not taking their aoe/multi-target abilities like divine storm, pestillence, cleave etc off their bars. Everything else seemed relatively manageable.

My findings as a Holy Pally are, duh, you have to play this fight like an arena match. That means that you MUST use indicators and alerts to better assist you in this fight. After having a number of other guilds on our server ask me how we "heal through" this fight, I first asked them what their healers use to indicate aggro on their raid frames. Most responded "what's that?" and I kicked a puppy. Basically, as paladins, we've gotta blow all our "OMGBOP!" cooldowns early and often.

• Grid shows you a red aggro indicator. If that red dot is not on the right brown, pink or red square then that square gets a Hand of Protection (immune to melee), Hand of Sacrifice (portion of damage transferred to pally) or Hand of Freedom (to help that raider get away faster). 
• CLEANSE! Jesus Tapdancing Christ, people: Grid shows both generic debuffs and boss-specific debuffs (with the addon GridRaidStatusDebuff). Get your mouseover cleanse macros set up properly and cleanse your brains out. 
• Help "Pain Train" the Main Assist. Ora2 gives us some pretty main tank frames that we can use to IMMEDIATELY see what our main tanks/assists are looking at. We generally make our focus-fire raider a smart and quick hunter. Whatever he looks at dies. As a Holy Pally, use those main tank windows to throw a solid stun, judgement, exo or shock on that target.
• Beacon yoursel, protect your squishies. I tend to hang back with the clothies and squishier raiders. I keep Beacon on myself and heal spam casters while also stunning any mobs that get too close. Don't get "Grid Vision" and play some zone defense. With Beacon on ourselves and non-stop heals on the raid, I'm pretty much indestructible on this fight. 
• PvP Trinket: Meh. I don't equip mine. If the healers in my raid can't cleanse a fear (IT SHOWS ON GRID), then I deserve to die for bringing such terrible healers. There are a few silences that are annoying as hell, but good vent communication ("Garreth stunned, heal Knoppix until I'm back.... Garreth back.") can cover the silence.

This is one of the most enjoyable fights in the whole game, partially because there is a definite "hump" that once you get over, you absolutely stomp the rest of the mobs. 

I put what I think are the specs to the npcs.   Correct me if I'm wrong.  Though not sure of the hunter and DK, but they prob don't matter.  DPS spec they all are!  ;p

is here. (anybody who can make this prettier...please help.)

Here's another vid, it's at the end.

Here's a comment from someone on the PTR:

"The encounter is very much like the "arena event boss" back in Magister's Terrace.

They play quite well actually, like using Dispersion when under fire or using Heroism and can't be tanked (as I said, like back in Magister's Terrace).
They can be crowd controlled but all spells only have their PVP durations and diminishing returns against them.

Boss is very easy and looks unfinished."

So if it's still like that, seems the only real strat is CC what you can when you can.    Snare / kite others if you can.   Be aware of Diminishing Returns!   Pick a target and focus it down asap.   Probably have to heal bomb / use external CDs on healers / squishies that are being attacked by them.   Also dispel/purge stuff, it'll be like pvp, there'll be BoPs  and stuff.