Dragon Age 2 - Act of Mercy is a main plot quest for the Templar Thrask. Players will encounter a large number of mage enemies in this quest, and be forced to make a number of important decisions, such as siding with the Templars or the Mages.

1. Head back home in Lowtown, and read the letters you got. Click accept on the “Act of Mercy” letter, and head out of the area to use the World Map.
2. Travel to the quest location marked with the “Act of Mercy” name under the Sundermount map area.
3. Follow the quest arrow. You will meet some minor enemy resistance on the way.
4. Speak with Thrask.
5. Enter the cave to speak with the mages.
6. Focus down the Apostate quickly in the first fight.
7. Continue on into the cave.
8. You will have no choice but to fight Decimus. Make sure to focus him down quickly. Just keep in mind he likes to teleport away, so look around and find him quickly when he does.
9. Return to Thrask, whatever option you chose during the dialogue with the mage woman.
10. Once again, you may choose to have the mages killed, or kill the Templars.
11. Head back out of the area, and then go to Lowtown at night.