Around 3/4 of the way through on level 12 the Galboss enemy will appear on your screen and this achievement will pop. You don't need to kill it, you just need to allow it to appear on your screen.
Tips to make the game easier:
Before the game starts you can go into Settings
then Game Settings
and change your maximum amount of lives from 3 to 5. You can also turn on select level. This will allow you to choose any level that you have reached. I would also recommend holding down the
button instead of pressing the
button because it shoots faster.