Tectus

Rise mountains.

Or should I say...

Ri-ri-rise-moun-rise-moun-mount-mountains.

Tectus heroic mode – Written bossguide

Ability overview
The Living Mountain: Tectus will start the encounter with a buff called "The Living Mountain". This buff will make him unkillable and cause him to regenerate energy (the rate of energy gained increases as Tectus loses more health.)
Accretion: Tectus periodically recieves a 5% damage increase buff. Damaging Tectus will remove Accretion stacks.
Earthen Pillar (one-shot): Tectus will raise an earthen pillar from the ground once he reaches 25 energy. The pillar takes a few seconds to surface, but it will instantly kill anyone standing above it. (massive AOE effect on the ground, a nono!)
Faultline (physical): Tectus will send a red cloud chasing a random player. The cloud itself deals damage to anyone standing in it, and will leave behind a red trail of bad stuff which also damages anyone standing in it.
Fracture (nature): Tectus will ocassionally cause a mini-earthquake on the ground beneath a random player in the raid, after a couple of seconds the spike will erect from the ground, dealing damage to anyone standing in it, also knocking the player up in the air.
Tectonic Upheaval (nature): Whenever Tectus reaches 100 energy he will start channeling an ability called "Tectonic Upheaval". While channeling, his "The Living Mountain" buff will disappear for the duration of the channel, making him vulnerable to shattering.
Shard of Tectus: When Tectus is shattered (he dies) he will split into two Shard of Tectus. They both cast the same abilites as Tectus but they deal less damage. Shard of Tectus inherits his "The Living Mountain" buff aswell.
Mote of Tectus: When a Shard of Tectus is shattered it will split into four Mote of Tectus. Just like a Shard of Tectus, a Mote of Tectus inherits all of the originals abilities.

Adds and add specific abilities
Night-Twisted Pale: When Tectus is in his original form, two kinds of adds will enter the fight ocassionally.
Night-Twisted Earthwarper:
Gift of Earth (physical): Night-Twisted Earthwarper will create a vortex at its current location that slowly travels towards Tectus. If the vortex reaches him he will gain ten stacks of accretion.
Earthen Flechettes (nature): Night-Twisted Earthwarper will deal damage in a cone infront of him.
Night-Twisted Berserker:
Raving assault: Night-Twisted Berserker will charge players at random, dealing damage to everyone in its path and to the player targeted by the charge.

Tactics breakdown
At the start of the fight you will want to position a majority of all ranged players in a clump at the far back of the room. Melee will ofcourse be standing behind the boss. Tanks will position Tectus in the middle of the room from the start. The ranged group has to be ready to move right as Tectus reaches 25 energy, as he will cast Earthen Pillar at that point. They can move either to the left or the right when the first pillar spawns but make sure to decide upon the placement before engaging the boss, as you don't want the pillars "all around the place". Aside from instantly killing anyone hit by a pillar, they are also massive and will LoS players.

The reason you will want a set pillar-placement direction is because of another ability Tectus casts called "Faultline". As mentioned above, Faultline is a red cloud that will fixate on a random players for a couple of seconds. And whoever becomes fixated should run in the opposite direction of the pillar placement team. If pillar group goes left, the person fixated by Faultline will go right. Also make sure neither melee nor the ranged stack right on top of eachother as Tectus will cast his "mini earthen pillar" called Fracture.

As mentioned in the abilites overview above, while Tectus is "whole" two kinds of adds will spawn ocassionally. The Night-Twisted Berserker is just a minor nuisance but should still be killed in due time. A perfect target to whittle down little by little using dots and such. The Night-Twisted Earthwarper should be killed at a rapid pace, although you don't want to send all dpsers on him as that would cause Tectus to gain accretion stacks. One important ability to keep in mind that the Earthwarper casts is "Gift of the Earth". You don't want this ability to reach the boss as it will give him ten stacks of accretion. Have anyone with some kind of soaking ability intercept this ability before it reaches the boss. Preferably not a tank, as the person who intercepts it will gain a debuff called petrification. Petrification will slow the affected players, and if Tectus attacks him or her he will absorb the petrification stacks, gaining health and accretion stacks.

You will have to deal with several sets of adds depending on how fast you can kill Tectus in his original form, so do put some pressure on them. As mentioned in the abilites overview above, Tectus starts the fight with a buff that makes him unkillable called "The Living Mountain". This buff however disappears when Tectus reaches 100 energy and starts to channel "Tectonic Upheaval". This is the only time where you can actually kill Tectus. Depending on your raids overall dps you might want to save heroism for when he casts Tectonic Upheaval at a low health percentage.

Once you've killed the original Tectus the adds will stop spawning, and two mini-bosses will pop out from his body called "Shard of Tectus". They both have the same abilites and buffs as Tectus and act the same way. They can be cleaved down and multidotted, but it's recommended that you kill them one at a time. When you kill a Shard of Tectus it will turn into four motes of tectus. Just like the shards, the motes will inherit all of the originals abilites. So killing both shards at about the same time would yield you a wooping eight Mote of Tectus, all of them casting one-shot earthen pillars, red clouds, earthen upheavals, and spikes. So by killing one of the shards first you'll only have to deal with a total of five "bosses", one shard and four motes. At this point the fight will turn into one big mess. It will be hard keeping your ranged group stacked and walking in set directions as there will be so many abilites going out, so its every man for himself at this point. Cleave/AOE down the motes and then proceed onto the second shard. Rinse and repeat and you've got yourself a boss kill! Grats.

Tectus can be challenging right now, but it's the challenge that makes overcoming it all the more rewarding. Fighting this stone elemental really reminds you not to take your loot for granite.