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