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
destroy 5000 blocks
complete 60 levels
play the game longer than 60 min
use the magnet 100 times
complete a level in 30 seconds
hit the ball 1000 times
destroy 1000 blocks
play with the last block and don’t hit it for 30 sec.
complete a level with no bonuses
complete a level without using the magnet
play the game longer than 5 min