Iron Dwarf, Medium Rare (25 player)

The best tip I can give to anyone who is trying to solo this achievement:

As long as you kill the Dark Rune Guardians within a half a second or so as Razorscale casts his flame breath you get the credit for the achievement.

If you can put out high enough dps you can get both achievements in one pull.

1. Start the encounter and aggro everything. There is no need to get the Guardians to low hp (unless you cant oneshot all them later). Make sure the engineers stay alive so that they can repair the harpoons.
2. This will take some time, but eventually you will have 25 Guardians alive (kill all the other mobs if you have trouble staying alive).
3. Shoot all 4 harpoons and position yourself between the harpoons and Razorscale's face.
4. If you want to do both achievements in one pull dps Razorscale down to 49%.
5. As Razorscale's stun wears off he will immediately start to cast his flame breath ability.
6. After he finishes the cast and you can see the flame breath animation instantly kill the adds. (I used Dragon Roar. Any strong, instant aoe ability should work).
7. If you timed it correctly you will get the credit for the achievement. (Achievement will pop up immediately, NOT after the boss kill).

Some notes:
I did it on a 581 ilvl fury warrior. I unequipped my legendary dps cloak and helmet with the legendary gem to avoid random damage to the Guardians. I used protection legendary cloak and helmet for more survivability. Defensive stance also helps.

If you can't survive long enough to get all 25 Guardians or you just want to get used to the timing just try a few times with less adds and then reset the encounter. (You can only reset it when Razorscale is on the ground and below 49%). The only other option is to die by aggroing all the adds and standing in the fire.

Last note: You don't have to kill all 25 Guardians in one pull. The achievement will never reset.

He's a SHE. She is Thorims proto drake mount, which is a broodmother.

Should work 100% for everbody:

- Talk to NPC
- Keep engineers alive so that they can repair all 4 harpoons
- Once the harpoons are ready you can just stand there and wait for the dwarfes to kill the remaining NPCs so that they automatically aggro you
- Wait until you have lots of dwarves hitting you (preferably 25 Guardians if you don't want to reset and do several tries)
- Shoot down Razorscale by clicking on the harpoons
- While he is in stunlock due to the landing, get him below 50% (unequipped my artifact weapon just to make sure he doesn't die)
- Now just stand in front of razorscale with all your dwarven friends and get a cup of tea because razorscale will do the rest for you and since you're probably lvl 110 you're not gonna loose much hp anyway

With this strategy you don't have to hit the dwarves at all and you don't have to care about his breath too much either.
The other strategies didn't work for me, so just do it like that and you should be fine.