Here is the full list of all 27 Hollow achievements.
Slain first Puker.
Collect all available weapons.
Kill wanton using gas tanks only.
Blow first destructible using gas tank.
Slain first wanton.
Kill wanton with single shot in a head.
Find all documents and notes.
Find all girl posters.
Find all collectable radios.
Sync all generators.
Fire-off all hands of wanton, than finish it with a headshot.
Slain first flying enemy.
Get killed more than 50 times.
Kill all monsters available in a game.
First bullet for Reaper.
Get caught by Reaper.
Finish Hollow game.
Unlock ending A.
Unlock ending B.
Finish game at HARD difficulty.
Finish game at HARD difficulty under 3 hours and do not use Save Discs.
Encounter Reaper for the first time.
Fix generator with fuse.
Go trouth all hallucination events in Laboratories.
Escape planet dream and get back to Shakhter-One deck.
Find way out of Cable Maze.
Kill burning Puker.