If You're Not Against Us...

<Race>. Have you been sent to speak with me? How long has it been since the master's demise on these very slopes?

• Yes, Blackhorn. I've been sent to request your aid, if you are willing.

My help? Have things really grown so dire?

<The distant flames flicker in Blackhorn's cruel, dark eyes.>

Tell me why I shouldn't let your world burn.

• You were a mortal once, Blackhorn. One of us.

  Mortal? Yes I was once mortal. Weak.
  
  You see my bonds now? These restraints are nothing compared to being shackled within a mortal coil.
  
  Even now the master's gifts stir within me, ready to be unleashed.
  
  No, <class>, my mortal days have passed, and if any flame of my former life still flickers within I would wish it extinguished. You'll have to do better than that, <race>.

  
  
  • You'll be destroyed if the Twilight's Hammer brings this mountain down!
    

    Destroyed? Yes, that's possible. At night I am haunted with visions of this would being torn asunder from within. I feel neither sorrow nor rage. Merely... curiosity.
    
    I served my master in exchange for power, <class>. But those you fight... they strive for oblivion. A strange motivation.

    
    
    • Will you help us to defeat them?
      

      Madness. Chaos. Much as I thrill to see the titans' work undone, I do wish to remain alive when the master returns. I will help you.

  • 
    
  • Where is your master now, Blackhorn? It's not too late to turn to the light...
    

    <Blackhorn strains against his bonds, for the first time visibly upset.>
    
    Redemption! You act as if there's an escape from the Burning Legion. So smug! As though your efforts a decade ago or in Outland have slowed the Legion a single iota! They will come, <race>. They will return. And I will be here to welcome them.

    
    
    • Assuming there's a world left for your legion to conquer. The Twilight's Hammer seeks to destroy everything.
      

      Destroyed? Yes, that's possible. At night I am haunted with visions of this would being torn asunder from within. I feel neither sorrow nor rage. Merely... curiosity.
      
      I served my master in exchange for power, <class>. But those you fight... they strive for oblivion. A strange motivation.

      
      
      • Will you help us to defeat them?
        

        Madness. Chaos. Much as I thrill to see the titans' work undone, I do wish to remain alive when the master returns. I will help you.

        
        

• You'll be destroyed if the Twilight's Hammer brings this mountain down!

  Destroyed? Yes, that's possible. At night I am haunted with visions of this would being torn asunder from within. I feel neither sorrow nor rage. Merely... curiosity.
  
  I served my master in exchange for power, <class>. But those you fight... they strive for oblivion. A strange motivation.

  
  
  • Will you help us to defeat them?
    

    Madness. Chaos. Much as I thrill to see the titans' work undone, I do wish to remain alive when the master returns. I will help you.

• Matoclaw believes that you may yet be redeemed. This is your chance to atone for siding with demons.

  <Blackhorn strains against his bonds, for the first time visibly upset.>
  
  Redemption! You act as if there's an escape from the Burning Legion. So smug! As though your efforts a decade ago or in Outland have slowed the Legion a single iota! They will come, <race>. They will return. And I will be here to welcome them.

  
  
  • Assuming there's a world left for your legion to conquer. The Twilight's Hammer seeks to destroy everything.
    

    Destroyed? Yes, that's possible. At night I am haunted with visions of this would being torn asunder from within. I feel neither sorrow nor rage. Merely... curiosity.
    
    I served my master in exchange for power, <class>. But those you fight... they strive for oblivion. A strange motivation.

    
    
    • Will you help us to defeat them?
      

      Madness. Chaos. Much as I thrill to see the titans' work undone, I do wish to remain alive when the master returns. I will help you.

The quickest way to get this quest done is to say he'll be destroyed by Twilight's Hammer (hinted in the quest text itself).

Aessina quest chain

1. The Fires of Mount Hyjal (breadcrumb quest)
1. Fighting Fire With ... Anything (kill 10 firestorms)

2. Save the Wee Animals (gather 10 animals)
2. Oh, Deer! (escort 3 fawns)

3. If You're Not Against Us... (Persuade Blackhorn)
3. Seeds of Their Demise (gather 8 Bileberries) 
3. A New Master (Use quest object on a dead orc)
3. The Name Never Spoken (toggle 3 objects)
   The Name Never Spoken
3. Black Heart of Flame  --.    (use quest object to call Thol'embaar and kill it)
                           |
4. Disrupting the Rituals  V  (kill 6 Inferno Lords)
4. Last Stand at Whistling Grove (need Black heart of Flame)(go to Taldros)
4. The Bears Up There (climb tree, save cubs)
4. Smashing Through Ashes (kill 8 Charbringers, IN HYJAL)
4. Durable Seeds (collect 10 seeds)                  |
                                                     |
      5. Fresh Bait (get 4 entrails from hounds ) <----->  6. Firebreak (kill 10 lava surgers)
      5. Hell's Shells (use bait, toggle Nemesis)          6. Prepping the Soil (toggle object, defend it)
      5. Tortolla Speaks -------------------.
                                            |
6. Breaking the Bonds (unchain Tortolla) <-----> 7. Children of Tortolla (kill 6 corruptors in lake, get ilvl 288 rare)
            |                                                 |
            .-------------------------------------------------.
                  |
                  V
8. An Ancient Awakens (go back to Hamuul Runetotem)

9. The Last Living Lorekeeper (go to Nordu)
9. Firefight (kill 5 tormentors)
9. Aessina's Miracle (go to Hamuul Runetotem, get ilvl 288 rare)

(The map of Hyjal phases at this time. The western part is no longer burnt. Tortolla moved)

10. Tortolla's Revenge (go to Tortolla)
    Tortolla quest chain begins