Here is the full list of all 21 Mad Father achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
Unlock image: "Charm Of Happiness"
See Bad Ending 1
See Bad Ending 2
See the True Ending
See the "If" Ending
Unlock a secret event...
Get chased by father
Give the dog a bone
Rescue the corpse from prison
Read mother's love letter in the second week
Receive a present from the mysterious plant
Help the hungry boy
Examine the specimens in the second-floor basement
Rescue the large man
Read the New Text on Anatomy
Help the eyeless girl
Read Maria's diary
Talk to the muttering old man
Unlock image: "It's Behind You"
Give the pendant to mother's corpse
Unlock image: "Mother's Portrait"