Phase One Abilities
Fearsome Roar is a frontal cone attack that applies a stacking debuff on affected players, causing them to take 25% more damage for each stack. This ability requires a tank switch, suggested number of stacks to switch on is 4 or 5.
Tail Lash is a tail attack that Thok casts, which deals a high amount of Physical damage to players located behind him, stunning them for 2 seconds.
Shock Blast regularly deals a high amount of Nature damage to random raid members.
Deafening Screech is a raid-wide damaging ability that Thok regularly uses. He uses this ability increasingly often as Phase One goes on, and the time of the next cast is indicated by Thok's increasing energy resource (which does not serve any other purpose in the fight). In addition to dealing a very high amount of Physical damage, this ability also interrupts player spellcasting.
Bloodied is a debuff that players receive when they drop below 50% health. The debuff has no effects whatsoever, but when a minimum number of raid members (5 in 10-man and 15 in 25-man) with the Bloodied debuff are within 10 yards of one another, Thok will enter Phase Two.
Variable Phase One Abilities
Each of the three instances of Phase One following the very first one will have slightly different abilities, depending on which NPC your raid frees during the preceding Phase Two. Specifically, Thok's Fearsome Roar and Shock Blast abilities will be replaced.
If your raid frees Akolik, the following happens.
Acid Breath replaces Fearsome Roar. Acid Breath is also a frontal cone attack, but it deals Nature damage instead of Shadow damage. It applies a stacking debuff on affected players, reducing their armor by 20% per stack.
Corrosive Blood replaces Shock Blast. Corrosive Blood deals Nature damage to random raid members, placing a 30-second DoT on them.
If your raid frees Waterspeaker Gorai, the following happens.
Freezing Breath replaces Fearsome Roar. Freezing Breath is also a frontal cone attack, but it deals Frost damage instead of Shadow damage. It applies a stacking debuff on affected players. At 5 stacks, the players become frozen in a tomb of ice, and raid members must destroy the tomb to free them. Being trapped in the tomb deals 5% of that player's health in damage every 2 seconds.
Icy Blood replaces Shock Blast. Icy Blood deals Frost damage to random raid members, placing a 15-second DoT on them. If players reach 5 stacks of the DoT (by being targeted 5 times before the DoT has a chance to wear off), they become frozen in a tomb of ice, and the tomb must be destroyed for them to be freed. Being trapped in the tomb deals 5% of that player's maximum health in damage every 2 seconds.
If your raid frees Warmaster Montak, the following happens.
Scorching Breath replaces Fearsome Roar. Scorching Breath is also a frontal cone attack, but it deals Fire damage instead of Shadow damage. It applies a stacking DoT on affected players, causing them to take a moderate amount of Fire damage per stack.
Burning Blood replaces Shock Blast . Burning Blood deals Fire damage to random raid members, placing a fiery void zone at their location.
Phase Two starts whenever the minimum required number of raid members affected by the Bloodied debuff are stacked together, and lasts until your raid frees an NPC and Thok kills them.
During this phase, Thok has two abilities. He will Fixate on random raid members, walking towards them. Throughout the phase, Thok is affected by Blood Frenzy, which causes him to deal lethal damage to any players who are in a short cone in front of him.
Thok remains fixated on the same player for 12 seconds, after which time he will change target. Throughout the phase, Thok's movement speed increases, such that after a while it becomes impossible to out-run him.
As soon as the phase starts, an add called a Kor'kron Jailer enters the room. This add has no real abilities to speak of (he has a standard temporary enrage effect that makes his melee attacks somewhat more dangerous), and upon his death, he drops a key. This key can be used to unlock one of the three cages found in the room, which are holding the three friendly NPCs that we have mentioned above. The player who loots the key is free to unlock any cage they choose. As soon as a cage has been opened, the NPC who was inside will perform a short role-playing segment after which time they will be devoured by Thok (who stops chasing his Fixate target), and Phase One starts immediately after that.
Fatboss suggest freeing Waterspeaker Gorai first, then Akolik and finally Warmaster Montak.