Note: This is a pre-release encounter guide, and as Halion hasnt been released yet this is all speculative... but anyhow, you get a hinch on what's coming and what to do rather than just "hey what happened? /die..
So, have a look on strategies, positions and enjoy the reading 
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Had a bit of trouble linking all the position images so if you want to have a look for yourself what phase 2 looks like just click on the link below (or perhaps easier, look how they do it on the video..
http://www.tankspot.com/showthread.php? ... re-Release
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Environment, Positioning, and Pull:
(1) After clearing the mini-bosses, you will travel to the center of the room and engage Halion. While it may seem like you have a wide area to work with, shortly after Halion activates he will put up an impenetrable circular flame wall that mirrors the circle you will see on the ground. So we encounter our favorite environment shape: the circle.
(2) Because of several abilities [notably his flame breath and several "void" mechanics], you will want to create as much space to work with as possible by tanking Halion parallel to the outside of the circle, right up against the flame wall [See Figure 1].
(3) I am uncertain if the final version of Halion will have a tailswipe or cleave [as of writing this guide he does not], but if so, the below positioning will also prevent any unnecessary damage from these types of ability.
(4) This fight requires two tanks.
(5) Starting positioning is simple enough. In fact, positioning is rather easy for the entirety of the encounter.
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Halion Abilities:
Halion has three phases: Physical Realm, Twilight Realm, & Split Realm. He has a total of 45.3m HP. Enrage timer unknown [Note: this shouldn't come into play as the Halion encounter is more about control than DPS]. I will break down each phase and the abilities there-in:
Twilight Precision
Persistent Aura.
Halion's insight into movement between phases allows him to deal unexpected strikes, increasing his chance to hit by 5% and reducing the enemies' chance to dodge his attacks by 20%.
Halion's version of the ICC debuff. Take that gear inflation!
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<---Phase1 [Physical Realm]--->
Phase one is a fairly straight forward DPS burn with spread out mechanics.
Flame Breath [25][10]
2sec cast. 30yd Range. Cone angle unknown. 10-15sec Frequency.
Inflicts 26250 to 33750 [10s: 17500 to 22500] Fire damage to enemies in a cone in front of the caster [Note: Exact damage figures subject to change].
A standard conical breath attack directed towards the highest aggro target. Don't stand in-front of the boss unless you are the tank.
Fiery Combustion, Mark of Combustion, & Combustion "Void Zone" [25][10]
Instant Cast. 30sec Duration. 20sec Frequency. Cleansable by magic or curse removal spells.
[Combustion "Void Zone": 40sec Duration. Variable Radius]
Engulfs an enemy target in flame, dealing 4000 Fire damage every 2 sec. Every time Fiery Combustion deals damage, it generates a Mark of Combustion charge on the target. When Consumption fades or is dispelled, it unleashes a patch of fire [25][10] [read void zone] proportional to the number of charges present at the time. Either curse or magic removal may cleanse this affliction.
Though the description of this mechanic may seem confusing at first, its execution is rather simple. Every 20sec a raid member [possibly ranged only, but unconfirmed] is given the Fiery Combustion debuff which deals damage every 2sec as well as building stacks of Mark of Combustion. When the debuff is removed via magic or curse removal a void zone is created proportional in size to stacks of Mark of Combustion. The coefficient on this is unknown.
Therefore it is important for the debuffed raider to quickly move away from all players where he will "drop" the void zone via a cleanse [magic or curse]. I will go over my recommendation for void zone placement at the end of this section. NOTE: It also appears the the "dropping" of the "void zone" has a significant knockback [unconfirmed 100yds] for all those who are in range at the time, making placement even more important.
Meteor Strike & "X" Fire Patch
Instant Cast. Approx 6sec "travel time." 35sec Frequency. ["X" Fire Patch: Duration approx. 30sec]
Deals 18750 to 21250 Fire damage to enemies within 12 yards.
Metoer Strike is cast at the location of a random raid member [melee & tanks can be hit by this, but it is unclear if that is always active or based on the number of raiders at range]. Upon casting, the area which the target was standing will be hit with Meteor Strike, causing the damage shown above. After the Meteor Strike hits, an "X" Fire Patch will spawn which will send out four lines of fire emanating from the epicenter all the way to the outer "fire wall." Note: This is not a "perfect X" like Coldflame during Marrowgar's Bone Storm [see video]. Damage while standing in the "X" Fire Patch is unknown, but not instantly lethal [damage seems to be comparable to Coldflame, if not slightly more aggressive].
Simply put, move out of the 12yard radius and avoid standing in fire. Melee should be ready to adjust if one of the fire "tendrils" meanders to their position. Tanks must also be ready to adjust the boss if it is cast on them. Moving 12yards back should alleviate any problems.
Phase1 Positioning Strategy Overview
(1) This is my recommendation for handling Meteor Strike and Fiery Combustion. As always, the best strategy is the one that works, so feel free to adjust this to your guild's playstyle. To start, have all ranged stand at max range against the fire wall like so:
Figure 1. Initial Phase1 Positioning
(2) The first type of ability you will encounter is Fiery Combustion. Simply have the infected raider move away from the raid like this:
Figure 2. Fiery Combustion Positioning
(3) The second ability you will encounter is Meteor Strike. If cast at ranged, have the range group shift 15 yards to the right like so:
Figure 3. Meteor Strike & "X" Fire Patch positioning for Ranged/Healers
Melee should be situated on the hind leg. If cast on melee, shift to the front leg like:
Figure 4. Meteor Strike & "X" Fire Patch positioning for Melee/Healers
If cast on the tank, simply walk back 15yards out of the range of Meteor Strike. Raid adjust accordingly:
Figure 5. Meteor Strike & "X" Fire Patch positioning for Tanks
At 75% Halion will enter Phase2 and will summon a portal that the entire raid save one tank and one tank healer must take to enter the Twilight Realm. The tank and tank healer left in the Physical realm will be responsible for holding the physical manifestation of Halion in position for Phase3.
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<---Phase2 [Twilight Realm]--->
As stated, at 75% Halion will begin Phase2 by entering a portal to the Twilight Realm that all raiders save one tank and one tank healer must enter. Its a good idea to leave your initial tank in the Physical Realm, while your "OT" picks up Halion in the Twilight Realm. During this phase, Halion cannot be damaged in the Physical Realm.
"Twin Shadow Pulsars"
Beam Duration 10sec. Frequency 30sec.
The "Twin Shadow Pulsars" periodically link, creating a beam of dark energy [Twilight Cutter] between them, causing those who cross its path to take 13,875 to 16,125 Shadow damage every second.
The first thing you should notice when entering the Twilight Realm are the two shadow orbs [which have the same model as the orbs from BPC in ICC] rotating on the outside edge of the room. 30sec after the activation of Phase2 [NOTE: not when you enter the portal], the "shadow pulsars" will link creating a beam that spans the diameter of the "room." The beam lasts for 10sec and is cast every 30sec. Basically 10sec of beam and 20sec without the beam.
Dusk Shroud [25][10]
PersistentAura.
An aura of twilight energy emanates from the caster, causing nearby enemies to suffer 4500 [10s: 3000] Shadow damage every 2 sec.
Everyone's favorite damage aura mechanic. Gogo gadget raid blanket.
Dark Breath [25][10]
2sec cast. 30yd Range. Cone angle unknown. 10-15sec Frequency.
Inflicts 26250 to 33750 [10s: 17500 to 22500] Shadow damage to enemies in a cone in front of the caster [Note: Exact damage figures subject to change].
Same mechanic as Fire Breath except more shadow-ery.
Soul Consumption, Mark of Consumption, & Consumption "Void Zone" [25][10]
Instant Cast. 30sec Duration. 20sec Frequency. Cleansable by magic or curse removal spells.
[Consumption "Void Zone": 40sec Duration. Variable Radius]
Engulfs an enemy target in flame, dealing 4000 Shadow damage every 2 sec. Every time Soul Consumption deals damage, it generates a Mark of Consumption charge on the target. When Consumption fades or is dispelled, it unleashes a dark explosion [25][10] [read void zone] proportional to the number of charges present at the time. Either curse or magic removal may cleanse this affliction.
Almost the same as the Fiery Combustion, except more shadow-ery. The one functional difference is those caught in the radius of the "void zone" when it is dropped are sucked to the middle instead of getting knockbacked.
Phase2 Positioning Strategy Overview
(1) This is my recommendation for handling the "Twin Shadow Pulsars" & Soul Consumption. As always, the best strategy is the one that works, so feel free to adjust this to your guild's playstyle. To start, have your tank set up Halion so he is behind the path of Pulsar1 all range and melee gather behind the path of Pulsar2 like so:
Figure 6. Phase 2 Initial Positioning
(2) Have the raid follow behind the path of the orb until it activates the beam. At this time you should have everyone go flat footed & pop heroism/BL. If executed properly, this is what your raid should look like at the beginning and the end of heroism/BL [Note you will most likely need to move a little bit counter-clockwise towards the end of heroism/BL]:
Figure 7a. Start Heroism/BL [0sec]
Figure 7b. End Beam [10sec]
Figure 7c. Pulsars pass by "un-beamed" [17sec]
Figure 7d. Pulsars begin 2nd Beam [30sec]
Figure 7e. End Beam. End Heroism/BL [40sec]
If I am correct with this positioning and timing, you will only need to "strafe" a little in the beginning to set up heroism/BL, and then once again towards the end of heroism/BL. At the end of Heroism/BL, reset back to Figure 7a positioning and repeat if you need more time to activate Phase3 [50%]. Smoke flares and the like will make this easier. If you are uncomfortable testing this you can always just continually strafe around the room counter-clockwise.
(3) Soul Consumption should be dropped by the wall like so:
Figure 8. Soul Consumption Positioning
At 50%, Halion enters Phase3 and will summon two portals to the Physical Realm that a few healers and half of your DPS should take. The remainder of your raid stays inside the Twilight Realm.
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<---Phase3 [Split Realm]--->
As stated, At 50% Halion enters Phase3. Half of your raid will be in the Twilight Realm while the other half will be in the physical realm. It is a good idea, if your raid is balanced, to have ranged take the portal and melee stay in the twilight realm as ranged will have more flatfooted time in the physical realm. The key mechanics are the same for those in their respective realms save one change:
Corporeality
Phases the caster between the physical and Twilight realms, altering his damage dealt and received in each realm according to his corporeality there.
Depending on how much damage is done to Halion in each realm alters the percentages of his damage done and received. This can range from equal damage done and received in both realms to 200%/400% increase in damage taken/received in one and 70%/100% decrease in damage taken/received in the other. Basically, your goal is to maintain equal DPS in both Realms by having Coporeality buff read this.
For the more visual learner, this is how the mechanic generally works [numbers not exact]:
(1) Phase3 begins. Halion at 50%.
(2) Halion at 40%. Both Physical Realm and Twilight Realm responsible for 5% damage of the total 10%. Halion receives and deals normal damage in both realms.
(3) Halion at 30%. Physical Realm dealt no DPS and Twilight Realm deals all 10%. Damage done/received increased in Physical Realm, while damage done/received decreased in Twilight Realm.
(4) Halion at 20%. Physical Realm dealt all 10% while Twilight Realm stops DPS. Damage taken/received normalized in both realms.
Again, the goal is for balanced DPS in both realms. NOTE: The Corporeality buff does not "slide" on health or time benchmarks, rather on damage done ratios. I am not certain what these exact ratios are, but, for instance, when Twilight reaches 2% more total damage done than Physical, the first "phase slide" will occur regardless of time and boss health.
When Halion's health reaches 0, you win. Collect your purples and rejoice.
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IMPORTANT NOTES:
(1) The key to this fight is raid positioning and proper DPS balance in Phase3 between the two realms.
(2) Make sure to leave one tank and at least one tank healer outside the portal for Phase2.
(3) Use heroism/BL in Phase2 as described above.
(4) Have Fire Aura/Totem running in the Physical Realm.
(5) Balance! Balance! Balance! Phase3 is not a DPS race, but a test on how well you can control your DPS. If one realm is dishing out more damage than the other, simply have them throttle back to maintain equilibrium on Corporeality.
(6) Corporeality "slides" based on damage done ratios, not at time or health benchmarks.
(7) I am uncertain if the timing of abilities will be different in 10s v. 25s. As soon as I can get that information I will incorporate it into the guide.
There are some interesting mechanics in this fight that should make it a lot of fun. Besides, who doesn't like a little sneak peak into some Cataclysm lore?
As always, feel free to add info to this post that will further everyone's understanding of the fight.
Good luck on the Halion Encounter and clearing Ruby Sanctum!
NEW! Check out this video which nicely shows the mini-boss abilities. Tactically, they're not very difficult, but its always good to have advanced information:
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