Channelers

Shadowbolt Volley

 A one second interruptible cast time, thirty yard AoE range, deals around 2000 damage.

Dark Mending

 A two second heal that is also interruptible, heals either the caster or another channeler within 60 yards for up to 32k HP.

Summon Burning Abyssal

Channelers can each summon up to around two Abyssals at a time, each lasting one minute.  These guys can be offtanked, banished, feared, frost nova’d, stunned, or trapped.

The Abbyssals also possess a fire blast attack that deals 3300 damage within a 20-yard range.

Soul Transfer

A buff that, upon the death of a channeler, enhances all the remaining ones by 20% damage and size as well as 30% casting speed, this does stack.

Magtheridon

Cleave

Deals up to 8000 or more damage on tanks, hits all in a frontal arc.

Conflagration

A small fire AoE on random parts of the floor.

Quake

50 second cooldown, first cast after 40 seconds.  A knockback that hits every players for seven seconds and interrupts spells.

Blast Nova

60 second cooldown, deals around 2500 damage every two seconds for a total of ten seconds to everyone within the lair.

Enrage

22 Minutes after the fight’s started, Magtheridon will enrage and kill everyone…

Phase One

Magtheridon’s lair is much like Onyxia’s, containing a few patrols of somewhat beefy guards preceding the actual boss himself
within a single immense room.  Once you’ve actually reached the bosses room you’ll see him being contained by five channelers, each next to a Manticron cube.

Once all the possible patrols and trash are taken down, it’s time to actually engage the boss encounter.  In order to actually release Magtheridon, you have to free him from the channeler’s barrier/hold over him.

Once the channelers have been engaged you have two minutes before Magtheridon will be released.

I’d recommend having a tank for each channeler as this allows you to tank them across the room and far away from one-another, preventing healing, and more importantly, the stacking of shadow volleys.

Hopefully you can drop all the channeler’s by the time Magtheridon becomes active, if not, make sure to at least still have a tank ready to pick the boss up anyway.

Phase Two

Once Magtheridon breaks his Banish, he will only begin to build threat once he’s actually targeted someone, allow him to begin the fight before utilizing your agro building moves on him.

This boss is quite tough, packing 4,750,000 health and a few rather deadly abilities such as quake and blast nova.  To deal with this you’ll have to correctly utilize the Manticron Cubes, a strategy that is explained below, otherwise this phase is somewhat simple.

Phase 3

Once Magtheridon has reached 30% he will shatter the walls of his lair, causing the roof to cave in somewhat and smash everyone below.  This attack deals 5260-6750 physical damage plus a 2 second stun to everyone in the raid.

After this and for the remainder of the fight the ceiling will randomly cave in on players, this Collapse kills everyone within an 8 yard radius of the impact.  Thankfully there’s a cave-in animation prior to the attack allowing people to move out of the way.

Other than that, beat him down.

Manticron Cubes

Every 60 seconds Magtheridon will begin to cast Blast Nova.  This attack is probably what causes 99% of the wipes when it’s allowed to complete, instead, stop this by activating all five of the Manticron cubes at once.

All the cubes must simultaneously be clicked (channeled) by players, this incurs both a damage penalty of 800 per tick and a mind exhaustion debuff once the players have deactivated the cube, this is a 90 second debuff that prevents usage of the cube within its duration.

Throughout both Phases 2 and 3 the constant quakes will make utilizing the cubes rather difficult, once every three or four usages of Blast Nova and quake the two will begin at the same time, with Blast Nova cancelling out Quake.

As using the cubes gives Magtheridon a 300% increase in damage taken it can be extremely desirable, however the stacking damage combined with the mind exhaustion debuff make it imperative to have back-ups in place to take over should the previous user need to back-off and heal.