Here is the full list of all 21 Cubicity achievements.
Win level without holding object
Win level without casting magnet
Beat level 3, In world 2, by casting only 1 portal
Obtain a New Weapon
Stuck in level for 5 minutes
Let seamus get bored
Hold 8 cubes at the same time
Get stuck on a level
Cast magnet 25 times in one level
Launched Cubicity for the first time
Win level 4, in world 1, without holding any object
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