Here is the full list of all 38 Possessed achievements.
The Chain Walk
Get Fucked
Hell's Design
Don't Look Down
Don't Fall
Eternal Torture
Hot In Here
Fat Motherfucker
Birds With Rockets
Welcome To Hell
Time To Die
6 Down
Nothing Can Stop Me
Stone Crusher
Katie I'm Coming
Nest Of The Netherworld
Taken
Not You Again
The Basement
More Ammo Needed
Now It's A Party
Hanging From A Thread
Join Us
Nurse To The Rescue
The Shitter
Healing Power
Crazy Lady
Didn't See That coming
Surprise
The Ol' Courtyard
Blow Holes
Not The Best Half
Stairwell Of Death
Evil Presence
Custodian Dan
Blow Some Shit Up
Meet And Greet
Humble Man