METAL GEAR SOLID 3: Snake Eater - Master Collection Version

This can be done on any difficulty. Just shoot the little frog statues. There is one on every map.

Here is the video I used as a reference. Credit goes completely to StoneSinner47 on YouTube: The trickiest ones are while Snake and Eva are on the motorcycle near the end. While the video guide shows this using the SVD sniper rifle, I prefer to use the RPG to hit the figurines since the blast damage will count. During this part, it can be hard to tell if you hit one because the sound the frogs emit can be drowned out by all the action. Save after entering a new location in the chase. If there is any uncertainty about missing one, reload and try again.

As with any achievement, there's always a small chance that it might glitch. I'd make two major save points that you don't override: one right before the driving section where it can be hard to tell if you hit one, and another during the final fight with the Boss. If it doesn't pop right at the end, reload and re-do the one with the Boss. If that still doesn't work, go back to the older save and make super-sure you hit the ones while riding with Eva.

EDIT: I can confirm that the karotans shot carry over between playthroughs. I played through once, swearing up and down that I had shot everyone. Going through again, I found out that I missed the one in torture chamber. Achievement popped immediately after.