I got this on level 4. I'm not sure if thats the first level you can get it on, but from what I could find it is. On level 4 when you shoot some enemies the Scorpion will appear once you hit an enemy enough. This is an unmissable achievement once you get to level 4, but there are a few ways to make the game easier if you stink. Before you hit
and start the game pause the game
and go to Settings
and then Game Settings
you can set the maximum amount of lives to 5 and turn on choose level. This will give you 5 lives compared to the 3 lives you would normally have. This will also allow you to choose a level if you get on to it. Meaning if you die on level 3 you can choose that level instead of restarting from level 1. This is a long guide to an unmissable achievement, but I'm just making it as easy as possible for you.
EDIT: Sorry I also forgot to say that holding down
will shoot faster than pressing