Here is the full list of all 13 Grey Cubes achievements. It takes around 4-5 hours to unlock all of the achievements on Windows.
play the game longer than 240 min
hit the ball 5000 times
complete a level with no bonuses
destroy 5000 blocks
complete 60 levels
complete a level in 30 seconds
play the game longer than 60 min
hit the ball 1000 times
destroy 1000 blocks
use the magnet 100 times
complete a level without using the magnet
play the game longer than 5 min
play with the last block and don’t hit it for 30 sec.