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