This is the last trophy/achievement that I missed in Dragon Age 2. It is called Demon Slayer and you must slay the ancient demon Hybris. This quest isn’t able to be done until act 3 so if you are in act 1 or 2 then don’t bother looking for these. You must find three Awiergan Scrolls and complete a quest for each one. The quest won’t start until you find at least one so don’t worry if it isn’t in your quest log right away.
Getting this trophy/achievement in Dragon Age 2 may contain spoilers so beware.
Alright first Awiergan Scroll we are going to get is in the Wounded Coast. Keep going and take the first south fork and check the dead end to find the Awiergan Scroll. After picking it up it will tell you to go to a hidden lair. In order to find the hidden lair take the southern path and head west. You will be attacked by some corpses and a Medan. Finish them and complete the first part of the Demon Slayer trophy/achievement.
The second Awiergan Scroll is in Sundermount. Right before you go into the Dalish Camp take the south fork and you should see the Awiergan Scroll. Grab it and it will give you a quest. Head through the camp and go up the mountain and you will be ambushed by some shades and an Arcane horror.
The last Awiergan Scroll is also in Sundermount. In the same spot you just got ambushed behind a wall you will find it. For this one you have to go up the mountain and go through it past the shrine. You will be ambushed by some different enemies. Kill them and head to Dark town to finish this.
Once in Dark Town go to Ander’s Clinic. Right next to it is the last Hidden Lair. Inside you will find Hybris. Kill Hybris to get your Demon Slayer trophy/achievement and be closer to getting 100% on the game.
I know there may be some more miss-able trophy/achievements in Dragon Age 2 but these are the only ones I missed if you need help with something else request it and I’ll post it.