Ko'ragh is the 6th encounter in the Highmaul raid.

For a more detailed view of his abilities please view the Dungeon Journal in-game, or click HERE to view it at WOWHEAD.

The primary mechanic of note in his encounter is an energy barrier that Ko'ragh surrounds himself with.  It absorbs all magic dmg, and the only way to remove it is to deal magic dmg to him.  So be sure to bring plenty of magic casters.

Abilities

1. Nullification Barrier - Energy barrier that absorbs all magic dmg (amount varies based on difficulty).  While surrounded by the barrier, he also gains Breaker's Strength, which increases his strength by 6% every 10 seconds.  Stacks, but once the NB is removed, the stacks of BS are also removed.
2. Charging - When the NB is removed, Ko'ragh will run to the middle of the room and re-charge his Barrier for 20 seconds.  Players (5 in LFR, 1 in Normal/Heroic, 2 in Mythic) who stand in the Charging rune effect will gain Caustic Energy.
3. Caustic Energy - The Player(s) that stand on the charging run with Ko'ragh will take moderate dmg every second and will received 35% reduced healing while standing in the rune.  This will bypass ALL immunities.  Caustic Energy will give the affected player their own Nullification Barrier absorbing up to 15 million magic dmg.  This will be required for another mechanic in the fight.
4. Volatile Anomalies - While Ko'ragh is re-charging his NB, 3 of these adds will spawn every 8 seconds.  When they are killed they will explode and deal moderate dmg.  Kill these in the Suppression Field to negate all dmg.
5. Suppression Field - Ko'ragh will charge a random player and smash the ground, dealing moderate/hight arcane dmg in an 8 yard radius.  This will leave a supression circle on the ground that silences all players in it and deals ticking arcane dmg.  Use this to silence Volatile Anomalies.

Now onto his primary attacks.  He will randomly "Expel" some form of magic... ie. Fire, Arcane, Frost, Shadow.

1. Expel Magic: Fire - places a fire DoT for 10 sec.  When this expires, this will explode dealing ~100k to all players within 5 yards.  SHOULD be able to be dispelled (should do so on melee).
2. Expel Magic: Arcane - Tank debuff - Targets current tank and marks their currently location every 0.5 secs for 10 seconds.  These locations will begin exploding after 1.5 seconds dealing MASSIVE dmg to all players within 5 yards.  Tank swap and the tank affected needs to run this out of the raid and along the wall until it falls off.  This will also place a debuff increasing phys dmg taken by 100%.
3. Expel Magic: Frost - Summons a Frost Orb that deals moderate/heavy dmg to all players.  Lasts 20 secs and slows movement of all players within 30 yards by 35%.  The 35% speed reduction decreases the further away you are from the orb.  If you are outside the 30 yard range you will not be slowed.
4. Expel Magic: Shadow - HEALER WARNING - Places a healing absorption on ALL players (amount varies per difficulty), blow healing CDs for this one.

Overflowing Energy - This is what you need the "player" Suppression Field for.  This will be a green orb that falls from the ceiling.  If it lands on a player, it will deal 1.5 million dmg to them.  If it is not absorbed, it will deal ~70k dmg to the entire raid.  There will ALWAYS be AT LEAST 1 more orb than is shields available.  So you need to ensure you get his barrier down, and have players get personal barriers to absorb the energies so the raid doesnt take too much raid-wide dmg and wipes.  If they get a full barrier they should be able to take 10 orbs.  This effect also ignores ALL immunities, so no deterrence or bubbles will work for this.

Summary

This fight is about burning down the Null Barrier fast, then having the required number (1 in Heroic) of player(s) stand with the boss to gain their own NB.  After that, their primary purpose is to ensure those player(s) always stand in an orb falling from the ceiling.  When the boss is re-charging, raid stand behind the Suppression Field on the ground so the adds funnel into it and burn them down ASAP in there to avoid raid dmg.  Stay spread for Fire, dispel off of the melee.  Tanks kite the Arcane debuff out.  Stay away from the Frost orb and healers blow healing CDs on Shadow.

Mythic Differences

In Mythic, 2 people can get the NB each time.  The boss will have a new ability called Expel: Fel, this will mark 3 random players for 12 secs.  This will create a line of fel energy between where the affecter player received the effect and where they effect expired.  This will last for 1 1/2 mins and deals 100k fire dmg to all players in it.  Think of it like the shadow shit on Blood Queen that you had to kite around.  He will summon the Overflowing Energy orbs at a faster rate.  He will also use Dominating Power, this will cause players who are absorb the Overflowing Energy orbs to become mind-controlled.  Thats not the only fun part... They become immune to magic, and can only be broken out once they are below 20% health.  So physical dmg is key here.  They will also spam cast Forfeit Power on the boss, which will take 5% of their shield and give it back to the boss.  So interrupt this.