WET

This achievement is quite easy. After you beat the game on normal you will unlock this mode. Beating the game this run through may be a good time to get Keep Your Balance (Get a balance of 50,000 Style Points) and also if best try to get Fully Loaded as well although it's hard because you can accidentally close the doors in the "stand offish" part.

For upgrades all you really need to do is upgrade the weapon speed on your pistol and your health since everything dies in one hit (upgrading other weapons is optional). Also in the parts where there are the doors that you have close (don't know whats it's called or if there is even a proper name =S) you can shoot them to close them so it makes them much easier.

There are only a few enemies that don't actually die in one hit. First the big guys with the machine guns. It'll take a number of shots to take them down for the little interactive cut scene to activate, But he starts running away after a couple shots. Second are the guys with the swords whom are armored. They won't die with one shot to the body but one to the head and they're dead. They're mostly on missions 12 and chapter 8 I believe.

To be on the safe side you might not want to use your sword very much. A good tactic is to just jump and spin around shooting your auto target will probably kill the enemies before you do. All in all this achievement is simple and doesn't really take that long if you're doing a speed run maybe around a few hours.

Hope this helps ^_^