Here is the full list of all 32 The Mildew Children achievements.
Finish chapter 12
Finish chapter 11
Escape Death's grip
Finish chapter 10
Help Lyrida overcome her fears
Finish chapter 8
Finish chapter 9
Finish chapter 7
Finish chapter 6
Finish chapter 5
Kill the hungry wolf
Finish chapter 4
Die while performing rites
Help your brother realize his plan
Finish chapter 3
Finish chapter 2
Meet a strange girl
Meet the Spirit of Apathy
Finish chapter 1
Try to walk away from Littlegrave
Remember Littlegrave's words
Meet the Spirit of Contemplation
Meet the Spirit of Loss
Meet the Spirit of Discord
Win a game of Bull's Feast
Make your apprentice cry
Overcome Death herself
Save the strange girl
Help the unlucky boy
Make no mistakes during the initiation
Make no mistakes on the night of the Dormition
Unlock the good ending