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