Here is the full list of all 27 A Walk in the Dark achievements.
Complete a Cave level without dying
Lead Bast to death 100 times
Disturb 10 butterflies
Kill Arielle on her first level while she's descending
Lead Bast to death 7 times
Destroy 30 dandelions
Catch your first Shiny
Complete a level under the par time
Lead Bast to death 1000 times
Catch 25 Shinies
Catch 50 Shinies
Catch 75 Shinies
Catch all 100 Shinies
Complete 25 levels under the par time
Complete 50 levels under the par time
Complete all timed levels under the par time
Complete all Cave flipper levels without dying
Catch all shinies, complete all timed levels under the par time and all Cave levels without dying
Complete all levels
Complete all levels in a unique speed run without dying more than 10 times
Complete all Cave levels
Complete all Forest levels
Complete all House levels
Complete all Spirit World levels
Complete all Strange World levels
Clean all smoke blocks in a level
Complete all challenge levels