Warhammer 40,000: Boltgun

Story-related, so cannot be missed. Simply complete all of Chapter 1, which consists of 8 Missions.

For the puzzle room in the Mission 'Sanctum Magistratum' (C1M8),

Obviously story related, this is obtained after completing the mission Sanctum Magistratum. To get past the puzzle room, only go through the portals with the chaos symbol above them. After 4 portals you should be on a platform and notice chaos symbols painted on the supports. Follow those to the final chaos portal (you’ll know it’s the last one because it’s rotated 90 degrees). Once you go through that, you’ll end up fighting the sorcerer boss, there is a secret damage buff at the top of the room. The achievement will pop shortly after killing him and the level ending.