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