Here is the full list of all 30 Downfall achievements.
You made Doctor Z really angry
You finished the game without using auto-save
You achieved the full, bad ending
You were really mean to Ivy
You blew out the candle and caused an unfortunate accident
You persuaded the Queen of Maggots to say her name
You spotted Slenderman in the forest!
You found some concept art in the lucky dip!
You achieved Downfall or Golden Ending without using tendency hints
You achieved the full, good ending
Susan built 2 weapons
Joe plays a tune on the piano
You read the third and Final Part of the letter
You read Part Two of the letter
Joe found Agnes' head on the desk in the manageress' office
Joe killed Agnes
You were given a motivational speech
You settled the matter with four Sophie's
You completed all the tasks in Helen Road
Joe killed the Receptionist
Joe examines knickers...a valid plot point!
You had a nice chat with Harrison
You explored all 4 floors of the hotel
Agnes persuaded Ivy to join her
You found a penis in the hotel garden
Agnes turned on the radio
Don't Cry, everyone dies...
You read Part One of the letter
You completed the tutorial
The cat ran away from Young Joe