Ace Annihilates's solution is spot on. I highly recommend reading his/hers first before reading mine. This is for those who keep getting Pink Gordos no matter how many times you try, even with Master Snares.
I placed down probably 15 Novice snares and 5-6 Master Snares all resulting in the same annoying Pink Gordo Slime. I tried everything mentioned in the above guide and nothing seemed to work. I searched online and found nothing. Here's everything I did to finally get what I needed.
First, I earned another key and opened the door to the Moss Blanket. I had been jumping over the door instead of opening it because I didn't want to waste a key. I figured maybe because the door is locked, the game doesn't recognize me having access to the Hunter slimes.
Second, I fed the Hunter Gordo located in the moss blanket 50 some chickens to make it pop. I figured, maybe I can only snare Gordo slimes that I've popped.
Location to Moss Blanket and the Hunter Gordo slime can be found in the videos below.
Lastly, I built 1 Master Snare and 2 Novice Snares and grabbed 3 Roostroos roaming the area. Once I was ready, I ran to the Moss Blanket and placed all 3 snares in the same area as the Hunter Gordo was located. Once I did that, I placed the Roostroos on the traps and jumped into the water which knocked me out. Once I awoke, the achievement popped.
Here's how you get to Moss Blanket:
Here's where the Hunter Gordo is located (You'll have to skip ahead in the video):
Finally, here is my clip of me unlocking the achievement: