You'll get this through natural progression through the levels, all you need to do is kill the monsters on the screen. I got this in the first world- Yello Jello.
Every reload of a level also helps towards this level. So, if you're having trouble 3 staring a level just think that it's not so bad as it's helping towards this achievement (and the other achievements Monster Hunter and Monster Nightmare).
If you really wanted to farm/grind this achievement you could load up a level and just play it 50 times if you're desperate to get it quickly.