Here is the full list of all 43 Agony UNRATED achievements.
Normal ending
Finish 4 level
Finish 3 level
Possess an ifrit
Kill an enormous chort
Possess a chort
Finish 2 level
Possess onoskelis
Finish 1 level
Try to push an onoskelis to the pit
succubus ending
Nimrod ending
Good and Evil (Unlock Evil and Angel ending)
Baphomet ending
Find all secret rooms
Find 2 red chambers
Find 2 gold chambers
Max out every skill
Unlock all letters and notes
Unlock all paintings
Unlock all comic pages
Unlock all characters in 3d viewer
Unlock madman ending
Unlock everything in gallery
Survive a level in Agony Mode
Find a peanut in the frozen caves
Push and kill an onoskelis
Find a secret room
Survive Baphomet bossfight
Finish 1 level as a succubus
Finish 2 level as a succubus
Finish 3 level as a succubus
Finish 4 level as a succubus
Use a finisher on onoskelis as a succubus
Kill a chort as a succubus
Kill 30 infants
Activate 30 collapsing floors and survive
Abort 5 pregnancies
Kill 15 spiders
Hold your breath for 666 seconds
Sacrifice 5 children at the altar
Finish the game for a second time as a succubus and kill 30 children
Hit a demon with a torch 20 times