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 9
Finish chapter 8
Meet a strange girl
Meet the Spirit of Discord
Finish chapter 7
Finish chapter 6
Finish chapter 5
Finish chapter 4
Finish chapter 3
Finish chapter 2
Win a game of Bull's Feast
Die while performing rites
Finish chapter 1
Remember Littlegrave's words
Try to walk away from Littlegrave
Meet the Spirit of Apathy
Meet the Spirit of Contemplation
Meet the Spirit of Loss
Kill the hungry wolf
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
Help your brother realize his plan