Norushen 10 man Normal Guide The Siege of Orgrimmar

Part 1 - Overview
The fights main mechanic is called corruption. You will start at 75 corruption, as shown on the extra powerbar that will appear on your UI. The starting level of 75 causes you to deal less damage to the Amalgim of corruption, who is the main boss. Corruption is removed by completing a series of tests. Ill go over these in specific later. Basically you click on an yellow orb and it takes you to a phased area where you deal with some mobs.
Removing corruption makes you more effective. DPS do full damage, healers get a healing done buff and tanks will take less damage.
There are also 2 kinds of adds who must be killed and have their mechanics dealt with.

Part 2 - Normal Phase
In this section I will talk about the normal phase in full. I will mention the test phase here, but will go into specifics in the next section.
First of all lets talk about tanks. There are 2 boss abilities that are relevant, Unleashed Anger regularly does 280k damage to the tank. The tank spwap ability is called Self Doubt which increases the damage taken from Unleashed Anger by 50% and requires a tank switch.
The nex ability is a raid wide one called Icy Fear. It will do increasingly high damage to the whole raid (in the normal phase) based on how low the Shas health is. In our group we stacked up and stayed as a group in order to more effectivly heal.
The bosses final ability is called Blind Hatred. He uses it every 60 seconds and it lasts 30 seconds. It is a large, instant kill, beam the origionaes from him and moves around the radius of the room. Think Drumus beam but without that horrific maze.
Once he hits 50% health he will gain "Frayed". At 50%, and each subsequent 10%, he will summon a large add called an Unleashed Manifestation of Corruption.
Adds
Now lets talk abot the normal phase adds. Due to a mechanic of the fith any damage done to adds will be mirrored onto the boss. No excuse for scumbag dps here.
Unleashed Manifestations of Corruption are spawned whenever a player in a test kills a Manifestation of Corruption, and when the boss hits 50, 40, 30, 20 and 10% health. They cast Burst of Anger which does raid wide damage. When they die they drop a void zone called Residual Corruption that does high raid wide damage until soaked by a player. When a player stands on it it dissappears and the player gets 25 corruption. This will put them at 100 corruption, meaning that they must do their "test" phase next to again be of use to the raid. Note that the mirroing of the damage to the boss only happens at the ones that spawn above 50%.
Finally there are small adds called Unleashed Essences of Corruption which spawn when a Essences of Corruption is killed in the test phase. They case "Expel Corruption" on the boss. This fires a kind of slow moving bolt at the boss. If it reaches the boss he will get buffed with fusion which increases his damage done by 5% for 15 seconds per stack.

Tying Together Phase 1
This fight is all about getting the purifying mechanic correctly. I will talk about the order that worked for us. The Unleashed Manifestations of Corruption drop the void zone as I said earlier. These give 25 corruption. Since everyone starts at 75 corruption and this will bring them to 100, the person who soaks it must be one of the next to go into the test phase.
We started by sending in 1 tank and 1 dps. Once the tank comes out they will have 0% corruption and can soak the void zone. Keep rotating in and out of the test like this, sending in a dps at a time and keeping the tanks able to soak the void zone.

Part 2 - Test Phases
These happen when a player clicks on one of the orbs.
DPS - There are 2 adds, Big ones and Small ones. Adds leave a globe on the floor when killed that reduces corruption - walk over them. The big add has a cone with is easy to avoid and the small ones shoot things at you which can be avoided. The small ones do a reflect shield.
Tank - You need to survive against a Titanic Corruption for 1 min. It does a Frontal Cone called Titanic Smash which must be avoided, a stacking DoT, an interruptible damage spell called "Hurl Corruption", a highly damaging ground attack that must be avoided called Burst of Corruption and finally piercing Corruption which does high damage and has to be tanked through.
Healer - The healer trial has 1 hostile mob and 3 friendlies. You need to heal the friendlies while they kill the hostile. Abilities are Dishearting Laugh which does 50k every 2 secs and must be healed through. Pit of Dispair which is a void zone and Lingering Corruption which must be dispelled of the player or one of the friendly adds.

Part 3 - Under 50%
When under you need to stack up the main group of players and burn the boss. At 50,40,30,20 and 10% hp he will spawn a  Unleashed Manifestations of Corruption. Since this does raid damage it must be killed immediatly, and its void zone must be picked up. Icy Fear damage will be high so healers should have cooldowns ready when needed.