There are 2 spots to best do them:
The first one is at the end of a stage in Chapter 3 where you'll first encounter Franken (Lure one away from the other so that he won't interfere).
And the second one is in the middle of the boss battle at the end of chapter 5.
Whichever you choose, this isn't at hard as it sounds. Actually, it's rather easy.. I made it on my third attempt when I first encountered them.
He will throw exploding creatures at you, and yes, you don't want to get hurt by them either. Since they explode and your ranged weapon can't kill them, you're best to avoid them!
Now for the actual solution:
You will need to use the wrangler 4 times on him. Before you can do that, you will need to stun him. You can do that by either punching him or wait until he does a jump-attack. He will be stunned as he reached the ground again.
Watch out for the exploding things whilst using the wrangler!
Once you've used your wrangler 3 times on him, he will stay crouched and release a big - and the last - amount of the exploding creatures. Just avoid them and use your wrangler the final time.
Note that this achievement won't unlock until you finished the level!