Here is the full list of all 15 Cube Creatures achievements.
Unlock 21st level
Unlock 36th level
Unlock 44th level
Finish all levels
Finish ten levels without death
Finish twenty five levels without death
Finish all levels without death
Dead more than ten times in one level
Dead more than twenty times in one level
Dead more than thirty times in one level
Dead in an old level
Dead very close to next savepoint
Knock down a round robot
Close to a creature but not dead
Active a trap but not dead