Here is a really simple way to earn this achievement without needing to obtain any special items found in chests etc.Requirements:
Discovered a Scorpion (any variation) using the Discovery Tool
Once you have obtained the 'Landscape Tool', you are going to need to select it using the Tool selection wheel by holding
. Once selected, simply enlarge the selection box and remove a chunk of the land to create a cube shaped hole in the ground. When done, you will need to access the Tool selection wheel again and choose the 'Discovery Tool' and filter through to the 'Creatures' section and choose any variation of the scorpion to place inside the hole you just created. I would advise spawning around 10 just to be sure, and then all you will need to do is just jump inside the hole and repeatedly attack the scorpions using the
button. Achievement will pop after killing your 7th scorpion.
Here is a visual guide for any who wish to use it...