Strategy:

He starts with 4 random adds. Possible known adds:

An Ogre - Melee add, Sheep him.

Gazakroth - An imp that spams fireballs, banish or kill it quickly.

Lord Raadan - A dragonkin that has flamebreath & Thunderclap, sleep/kill him quickly. Killing him is highly recommended.

Darkheart - An Undead Wraith melee and instant casts, shackle him.

Alyson Antille - A Blood Elf healer. Interrupt her heals/kill her quickly.

A Serpent - Poison bolts. Sleep it/kill it quickly, as for Raadan. If you kill it druids won't have to shapeshift.

People seem to kill 1 or 2 of the adds before focusing on the boss.

Malacrass:

Does a nasty dot that lasts for approx 15 sec and deals roughly 300-400dmg per tick.

During the fight randomly he will Soul Drain 1 random person, he will take on 2-3 abilites of that persons class. He will continue to use these new abilities till he Soul Drains another victim and repeats a new cycle of attacks.

Every minute or so he will drain everyone of their power by 1% and giving it to himself, thus increasing his size and his damage by 10%.

Tank and spank and deal with the new abilities he may gain.

Possible Soul Drains (Seen and or Heard, not sure if its spec Dependant or not):

Druid - Lifebloom, Thorns  Heals for a large amount 
Hunter - Various Traps  
Mage - Fireball, Frostbolt, Frost Nova  
Paladin - Consecration, Holy Light  
Priest (Holy/Discipline) - Heal, Mind Control  
Priest (Shadow) - Mind Blast, Shadow Word: Death  
Rogue - Blind, Slice and Dice  
Shaman - Fire Nova Totem, Healing Wave  
Warlock - Curse of Doom, Rain of Fire  
Warrior - Spell Reflection, Whirlwind