Dragon Age 2 - Mine Massacre is a side quest in Act 3. For this walkthrough, players will encounter arguably the hardest boss in the game, a High Dragon, in order to stop it from slaying miners. The rewards and loot from this quest are quite valuable.

1. To acquire the quest, either speak with Hubert in Hightown, or visit the Bone Pit (outside Kirkwall) in Act 3.
2. Follow the quest arrow down to the mine to start the fight with the dragon.
3. Note: this fight is very difficult, and as such has a lot of points to keep in mind, just like the Ancient Rock Wraith fight.
4. For starters, make sure to have a lot of health/mana/stamina potions ready. You will need to use them many times throughout the fight.
5. Other useful items includes gear that has fire resistance on it and Fire Warding Runes in all possible armor slots for all your party members, which will greatly reduces the damage. Reviving potions can also be quite useful.
6. Another great way to reduce the damage for this fight is a fully upgraded Arcane Shield spell, and the Elemental Aegis talent for your warrior tank.
7. Your group composition should consist of 1 or 2 warriors, 1 or 2 mages and ranged DPS. You will put 1 tank on the dragon, use 1 or both of your mages for support, and a possible second tank for the minion phase. Ranged is generally favored over melee in this fight, as they can attack the dragon in the minion phases, and aren't so susceptible to AOE attacks.
8. Note: You will always want Anders in your group, as he will have the "Regroup" spell which can ressurect dead party members and as such is very helpful for this encounter.
9. Note: The dragon is highly resistant to elemental spells, so mages with Cold/Spirit spells are much more useful here.
10. After the short cutscene, immediately put your tank on the dragon, and start damaging it.
11. Note: If you do have more than 1 melee, make sure to put him or her on the side of the dragon, as the dragon will cleave the targets in front of it.
12. Note: Moving your tank around the dragon will force the dragon to move as well, meaning that it has less time to attack. Do this if you feel your tank is taking too much damage.
13. Note: You will have to pause a lot during this fight to micromanage your party members. Using stamina and health potions on your tank in particular is very important, as healing from your 1 or 2 mages will not be enough.
14. Note: If you have a second warrior and he has the taunt talent, you can use this for a small advantage. Whenever your main tank starts dying and you can't heal or potion him, you can taunt off to allow your tank to heal up before taunting the dragon back.
15. When the dragonlings spawn and the dragon flies up, AOE them down. Make sure to keep them off your mages, and try to avoid the fireballs being launched by the dragon.
16. Note: your party should always be as spread out as possible to avoid AOE damage. Note however that this makes it more difficult for your tank to pick up the minions during the minion phase.
17. After some time, the dragon will fly off the rocks above and land. Make sure to get away from this spot, as the dragon will cause damage to anything near it's landing spot.
18. The High Dragon will continue to fly up to the rocks and spawn minions a few more times in the fight. Keep in mind that 1, and then 2 normal Dragons will be spawned in these minion waves, so they have to be tanked and taken down quickly, as they will kill your mages even faster than the dragonlings.
19. After you slay the dragon, loot it, and return to Hubert in Hightown for your reward.