Horridon

LFR:
This is a very chaotic fight, which doesn't favor LFR, so good luck.

Tanks: One tank on the boss, the other on the adds. Switch after each set of adds die (when the boss charges a gate and closes it.)

Boss tank: Keep the boss in the middle as much as you can, turned so that its side is facing the raid. He does two abilities of note, Triple Puncture which puts a stacking debuff on you, and Double Swipe, a front and rear cone ability that you can (and should) sidestep away from.

Add tank: The adds come out over time and are spread out, try to pick up as many as possible, but it's hard. None of them hit terribly hard in LFR, so don't sweat it if a hunter or warlock gets frisky with their pets. Put a skull on the Dinomancer when it spawns and interrupt its heal.

When Lord Jalak comes out, he needs to be picked up and focused down.

DPS:
Kill adds, interrupt when you can, and don't stand in anything. Don't ever stand in front of or behind the giant triceratops. Kill order is:
Dinomancer > Other adds > War-God Jalak > Horridon

Interrupt Dinomancer's heal.

When a Dinomancer dies, it drops something called an Orb of Control. If you see it, click it. That's what shuts the gate and stops that wave of adds.

Healers:
Tank damage increases with stacks, otherwise it's standard fixing problems caused by people not paying attention, standing in crap, and failing to interrupt. If you want to pretend that you're surprised by this, we'll all play along.

tl;dr verison:
Tanks - One on the boss, one on the adds. Swap after each set of adds. Boss tank, avoid Double Swipe.

DPS - Dinomancer > Adds > War-God Jalak > Boss
Interrupt Dinomancer's heal. Click on Orb of Control once Dinomancer dies. Don't stand in crap.

Healers: Heal, dispel what you can, nothing particularly surprising in this one.

Macroable:

/raid Tanks - One on boss, one on adds. Swap after adds.
/raid DPS - Dinomancer > Other adds > Jalak > Boss
/raid Interrupt Dinomancer's heals and click on Orb of Control once Dinomancer dies. Interrupt anything else you can.
/raid Heals - Good luck.


He'll open the door~

Jalak gets on the floor~

Everybody DPS the dinosaur!

In 10 man mode we used 2 tanks, 3 healers and 5 DDs.

You have to deal with some abilities that are pretty easy to handle during the whole encounter and some additional abilities, while a specific door is open. The bossfight can be separated into the add or door phase and the burn phase, after the doors are destroyed.

Abilities used through the whole fight:

• 
  
• [spell=138768] is an attack against the current tank, dealing high damage and leaving a stacking debuff, increasing damage taken by [spell=138768] by 10%.
  Switch at a stack value, that your tanks and feel comfortable.
• 
  
• [spell=136739] is a frontal and rear 35° cone attack in rapid succession. Therefore do not stand before and behind the boss.
• 
  
• Sometimes he uses [spell=136769] at a random raid member, with [spell=136739] directly following.
  The targeted person should run outside the group and not face head or tail towards the group.
• 
  

Phase 1:
During the encounter trolls spawn at one door with a fixed sequence, starting at the door to your left, when you enter the room.

• 
  
• At each door spawns after some waves a [npc=69221] who tries to heal Horridon and has to be killed in order to close the door. The Dinomancer has always top priority because it stops the other adds from spawning.
  To destroy a door, the Dinomancer has to be brought below 50% HP forcing him to transform into his [spell=137237] which results in dropping an Orb of Controll, that can be used to force Horridon to destroy the door.
• 
  

Now, let's have a look at the certain waves:

1. 
   
2. The Farraki (Sand Trolls)
   
   • 
     
   • [npc=69172] have low HP and spawn until the door is destroyed. They sometimes use a cast called [spell=136708] stunning their target for 10 seconds. They have a pretty low kill priority.
   • 
     
   • [npc=69173] have also low HP and spawn until the door is destroyed. They should die by cleaving attacks.
   • 
     
   • Three [npc=69175] spawn during this wave. They are the dangerous Farraki, creating growing void zones called [spell=136725] and casting [spell=136719] which has to be dispelled, if the cast is completed. Focus at high priority.
   • 
     
   
   
3. 
   
4. The Gurubashi (Poison Trolls)
   
   • 
     
   • [npc=69167] have high HP and spawn until the gate is destroyed. They have the lowest priority and use an attack causing a medium bleeding effect. ([spell=136653])
   • 
     
   • Three [npc=69164] spawn and have a very high killpriority. Interupt their cast [spell=136587] at all costs because it is a stacking raidwide poison dealing insane damage at high stacks.
     Also they can summon [npc=69314] which have very low HP but also cast the poison volley and have to be killed asap. Each time one [npc=69314] is summoned a green void zone called [spell=136645] is created.
   • 
     
   
   
5. 
   
6. The Drakkari (Undead Frost Trolls)
   
   • 
     
   • [npc=69184] and [npc=69185] spawn until the gate is destroyed. They attack random targets and apply a disease called [spell=136710] which has to be dispelled.
   • 
     
   • Three [npc=69178] jump into the arena and have to be focused. They do high tank damage and have [spell=12294]. In addition they summon near static [spell=84714]s dealing high damage to players standing close.
   • 
     
   
   
7. 
   
8. The Amani (Forest Trolls)
   
   • 
     
   • [npc=69169] with high HP spawn until the door is destroyed. Low priority.
   • 
     
   • [npc=69168] with low HP and a dangerous fireball spawn until the door is destroyed. High priority.
   • 
     
   • Three [npc=69177] spawn and have to be tanked in a way that the do not face the raid because they use a cleave attack with high damage. When they die, the [npc=69176] who was riding the bear attacks.
   • 
     
   • [npc=69176] use dangerous spells and have a high priority.
     They cast a [spell=136480], therefore the raid has to be spread out.
     They curse random players with [spell=136512]. This has to be dispelled and is on some classes with lots of abilities in a short timeframe deadly. Each attack has a 50% chance of inflicting the cursed target damage.
     Finally they summon [spell=136487]. DO NOT stand inside the totem range.
   • 
     
   
   
9. 
   

Phase 2:
When all doors are destroyed and Horridon is below 30% HP [npc=69374] spawns in the middle of the arena. There are 2 possiblities, how to finish the encounter, depending on your setup:

1. 
   
2. Kill [npc=69374] and have Horridon in a softenrage. This puts a lot of pressure into tankhealing, but reliefs your group heal.
3. 
   
4. Offtank [npc=69374] while you kill Horridon. This is probably more used in 25 man raids, because Horridon has actually low HP in 25 man in relation to 10 man. This tactic puts more pressure on group healing and forces the DDs to burn through this phase.
5. 
   

In either tactic the boss takes an additional 200% of damage, because of 4 stacks of [spell=137240] from destroying the four doors.

My group has chosen the first possibility for the kill.

A video of our kill can be found here: http://www.youtube.com/watch?v=SvdzGplyCu0
It's not the best gameplay, but it should help to visualise the description given.
I used Dream Theater as music for the video.