Pillars of Eternity

This achievement is related to 2 separate quests and requires you to slay 2 dragons, the Sky Dragon and the master below

[b]MISSABLE:
BOTH the dragons MUST be killed,
It is very easy to persuade one of the dragons to leave, this will VOID the achievement. They must be killed

Scroll further down for advice on defeating ADRA, scroll to end for video of Adra. as the other dragon is very easy this solution focus's on the very difficult adra dragon

The ADRA dragon is very diffcult and requires the player to understand the games mechanics and how to maximise team abilities. Therefore I recommend waiting until you are Level 16 before tackling the Adra Dragon. It can be done before then but by then you should understand the games mechanics and how to maximise your characters abilities.

The sky dragon is easy to kill(in comparison to Adra) it took me around 10 seconds, as it is related to a main quest called The nest above the Cloud, you should be able kill this dragon from around level 8-10. The fight will be more difficult under this level.T he quest can be obtained by either talking to the God Hylea during the Council of Stars main quest or by talking with Casfath in oldsong.

Adra dragon on the other hand is one of the most difficult enemies in the game, so i will devote most time on how to slay this beast.

The Master Below
Adra dragon is the Master below and you reach it by fighting your way down to level 15 of the the Endless paths it is incredibly important and makes this battle so much easier if when during dialogue with the dragon you agree to help him. This allows you to attack the dragon at your convenience and more importantly to position all your party.

preparation
each party member should have at least 5 major endurance potions, tanks should have 10, craft 10-15 paralysis scrolls, craft 10 maelstrom scrolls, equip Beast killer upgrade enchantment on all primary weapons, iverras Divine Helmet on a tank.

Party
I strongly recommend that you you visit a merchant and retrain your Chanter so he can summon a Drake and focus on support chants, and retrain your Tank to maximise passive abilites and bolster defences and priest for healing and buffs. The beast slayer ability is really helpful as Dragons are classed as Beasts this increases damage by 25%.

Recommended Squad
Tank (Eder), Kana (Chanter), Durance (Priest), Grieving Mother (Cipher), final member optional Either another tank or Ranger.

make sure your 3 magical characters have the ability to cast at least level 4 scrolls, preferably level 5 . Equip each Caster with 5 paralysis scrolls and 5 scrolls of Maelstrom.

Strategy
turn Fast mode off, make sure the battle is in either normal or slow mode by pressing .

Position your party so they encircle the dragon, keep ranged characters out of the tails reach, I had 2 tanks, one I sent to the front and the best I sent to the rear, (keep your chanter well away).

when you have positioned your party make A Save This saves so much time of you have to reload

Initiate the battle when your party is positioned. To make this battle really simple have your best casters use scroll of paralysis, alternate between the two every 5 seconds, have the third cast scroll of maelstrom every 10 seconds, make sure you give each party member commands dont rely on Ai, summon your chanters drake, also use any Idles you have collected to summon other help.

The dragon should be focused on your tank giving your 3 casters who should be set back and set apart from each other free reign to use there scrolls, the scroll of maelstrom will inflict massive damage, also utilise any spells or buffs. The key to victory is slowing the battle down and issuing orders directly, take note of endurance levels and use a potion when you see fit.

Here is a video for those who prefer visual aids.
If the achievement does not unlock after defeating the Adra dragon it is likely that you asked the Sky dragon to leave. If you were offline or your internet dropped it should unlock within 48hours