In Kirkwall in Dragon Age II, there are random group encounters of enemies in Docks, Hightown, and Lowtown at night during all three Acts who ambush Hawke and his/her companions. While some only appear in later Acts, it is possible for early gangs to appear all-throughout if you do not defeat them.
When you have defeated a gang you are able to collect a reward from a NPC called A Friend. This is not marked on your map or journal as a quest, but is a bonus for cleaning the streets. A Friend only appears at night, in the back room of The Hanged Man. She will continue to give out rewards each time the player clears out a band of thugs in the subsequent side quests.
These groups are encountered during Sketchy on the Details:
- Antivan Assassins
- Carta Loyalists
- Denerim Avengers
- Qunari Death Squad
- Rivaini Legendary Beard