Full list of all 26 I'm on Observation Duty 6 achievements.
The base game contains 20 achievements, and there is 1 DLC pack containing 6 achievements.
Meet the Bruxsa
Meet the Crawler
Witness the secret ending
Complete "Pool"
Meet the Marionette
Meet the Stalker
Complete "Summer Cottage"
Meet the Nixie
Meet the Lumberjack
Complete "University"
Meet the Principal
Complete "Hospital"
Meet the Patient
Complete "Hotel"
Meet the Banshee
Complete "Train"
Meet the Director
Meet the Passenger
Meet HUGE MAN
Meet the Doctor
Complete "Hotel" on Hard difficulty
Complete "Train" on Hard difficulty
Complete "Pool" on Hard difficulty
Complete "Hospital" on Hard difficulty
Complete "University" on Hard difficulty
Complete "Summer Cottage" on Hard difficulty