Here is the full list of all 12 Alter World achievements.
Complete 10 Levels
Complete 20 Levels
Complete 30 Levels
Complete 40 Levels
Complete 50 Levels
finish game with first ending
Finish game with second ending
Brave enough? die 100 times!
Jump! Jump! Jump!...and again Jump!
Forever gone to Alter!
last death!
Meet developer!