Here is the full list of all 18 A Timely Intervention achievements.
Hydra Defeated
Orc Leader Defeated
Troll Defeated
Frost Dragon Defeated
Ancient Crypt Found
Borehole Worm Defeated
Underworld Demon Defeated
Argmahn Defeated
All Stonebarrow Lake Foes Killed
Secret Passage Found
A Timely Intervention
All Along the Watchtower
Artifact Defeated
25+ Secret Rooms Found
1000+ gold
5000+ gold
6+ Sidequests Completed
12+ Sidequest Completed