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.
complete a level in 30 seconds
hit the ball 5000 times
destroy 5000 blocks
play the game longer than 240 min
complete 60 levels
use the magnet 100 times
play the game longer than 60 min
hit the ball 1000 times
destroy 1000 blocks
play with the last block and don’t hit it for 30 sec.
complete a level without using the magnet
complete a level with no bonuses
play the game longer than 5 min