Left 4 Dead 2

The best way to do this is on Dead Center, as you start with a fire ax. And set the difficulty to easy so you can do this achievement at the same time as CONFEDERACY OF CRUNCHES (Complete a campaign using only melee weapons)

When killing the zombies aim above their neck, and you should get a decapitation. Do this 200 times and you'll get the achievement.

Going through the whole Dead Center campaign and having a good aim at their necks should net this achievement in the one go through, but if it doesn't just remember it has to be an edged weapon for decapitations (the Fire Ax, Machete, or Katana will all work). Just grab one of those weapons on your normal playthroughs and go for more decapitations when you can.

The achievement doesn't have to be in one campaign, just overall you need to get 200 decapitations.

Hope this helps. :)

Use an edged weapon, axe, ninja sword, or machete. Then when facing enemies, aim so your cross hair is at the top of their heads. This will almost always decapitate them. If you are having trouble, try shooting car alarms or getting Boomer bile on you to draw enemies in a tight circle around you then you can adjust your aim accordingly with trial and error.

Decaffeinated?

Video says all [:

Hey guys this is pretty easy method In the video he does use a gun but get an axe or weapon that can slash heads off and use the technique in the video.