Here is the full list of all 18 I Wanna Build a Robot achievements.
You've finished the game !
You've got the legs!
You've got the arms!
You've got the head!
You've got the wrong head!
You've found a secret path!
You've found all the secret paths!
You've got the stick!
You've got the stone!
You've chosen the coward's way...
You've chosen the Heroic's way!
You cleared the first hub.
You cleared the first level.
You cleared the second hub.
You cleared the second level.
You cleared the third hub.
You cleared the third level.
You cleared the boss level.