Only two guilds in the world have killed Magtheridon, and after reading a write-up of the fight, I'm not surprised.
Basically, as I understand it, there are five warlock/channelers with about a couple hundred thousand HP each. They hit for about 5000 on plate armor. They also do a shadowbolt volley for 3k, summon infernals who one-hit anyone besides a tank, and heal each other. When one of them dies, the others gain a increase of 33 percent damage and increase in casting speed. After two minutes of fighting the channelers, Magtheridon becomes active. He hits for about 700-900 on plate and cleaves. He also has two special abilities: a knockback that pushes everyone to the walls of the room, and a fire nova that ticks for 2.5-3000 damage every two seconds and lasts for ten seconds.
The "trick" to the fight is that there's five boxes in the room, each guarded by a warlock/channeler person. If five people click on the box and channel it at the same time, it stuns Magtheridon and lets you do 100 percent more damage to him. However, controlling the box deals 700-800 damage to its controllers, and then you can't control one again for 90 seconds.
My opinion: The hell? How can you even do this without bringing a seriously stacked raid? Do you have to enslave or banish all the infernals with six warlocks, or mind control the channelers with five priests? Nihilum and Death and Taxes are being quiet about their strategy, but this TOP SEKRIT missive from DNT raid chat shows them having a rough time clicking the boxes.
Do you have any idea of what it would take to beat Magtheridon? Theorycrafting is always welcome!