Here is the full list of all 21 Cubicity achievements.
Win level without casting magnet
Stuck in level for 5 minutes
Win level 4, in world 1, without holding any object
Let seamus get bored
Win level without holding object
Beat level 3, In world 2, by casting only 1 portal
Obtain a New Weapon
Cast magnet 25 times in one level
Hold 8 cubes at the same time
Get stuck on a level
Launched Cubicity for the first time
Find our logo
Let the cubes fly!
Beat level 11, In world 3, By casting only 1 portal
Beat level 2, In world 4 unofficially (w)
Merge 11 objects
Get to 10 hp without dying !
Find the evil scientist portrait
Change 6 cubes into magnetic cube
Get to Egypt
Obtain all the Achievements in-game