Here is the full list of all 21 Occult achievements.
start a four-player game
caught 25 spiders
complete the game alone
found the phone and answered the call
kill with train
defeat the evil
kill mediums
sat in the closet for more than a minute
big bang
collected 10 jewelry
died from the fall
mirror quest finished
killed the Spiderlady
open 3 locked doors
25 window jumps
first time stunned by a monster
throw a friend out of the cupboard 5 times
open lockers and drawers 50 times
helped a friend get up
start a game together
5 minutes to stand by the car