for this achievement you need to find 4 rat kings
the first one is in the level E0M1
first, you need to find the cheese that is located in the Sloppo's freezer
then you go back at Uncle Frank's Big Dump with the cheese to the first rat king.
the rat king is located in a hole to the left, right after the fence after you get the S Blade.
The second on is in the level E0M3
you will find the cheese in a secret area at the bottom of the stairs after opening the door that led to the surface. (the door that need the psycho key to open after beating the toilet boss).
then bring back the cheese to the rat king that is hidden on the roof of the Fun Zone.
the third one is in the level E0M6
the cheese is hidden on top of the roof of the tallest house in the second trailer park. (you can't miss it)
the rat king is hidden behind a fence near the power house. (the hidden spot is where you find an already exploded red gas tank.)
the last one is in the level E0M7
the cheese is hidden behind the hacker blood pool where you get the psycho key.
the last rat king is hidden in the Spinning Barf Ride for kid. (the one closed for maintenance)
there's a hole behind it where you will find the last king.
hope this guide help
this should unlock the achievement after giving the last cheese.
i wanted to make a full visual guide but TrueAchievement won't take the capture i took on PC.
sorry if there's any spelling mistake. English is not my first language.