Here is the full list of all 27 Stay in the Light achievements.
Get 25 treasure objects
Solve Puzzle Room 3
Get killed in a violent manner
Solve Puzzle Room 1
Throw the Torch at Him
Survive being attacked, don't die
Complete the first level
Get the first magic mirror
Get 5 treasure objects
Get 50 treasure objects
Get 100 treasure objects
Get 200 treasure objects
Solve Puzzle Room 2
Solve Puzzle Room 4
Complete level 5 of the game
Light 10 Torches
Light 50 Torches
Use your chalk a lot
Speak to all the skeletons
Refuse the offer he gives you at the end
Accept the offer he gives you at the end
Get the ultimate magic mirror
Complete a level with no torches
Use the Mirror in a way nobody expected
Find and loot the ultimate hidden treasure room
Make it all the way to the end
Get one of each kind of treasure in the game