kill.switch

Level select:
Successfully complete the game under the normal or hard difficulty setting to unlock an option that will allow you to pick any level in the game.
Magicmomentsandu.

Hint: Grenades:
When on any level and there are two enemies talking to each other, throw a grenade (for example at the beginning of the Think Like A Gun level). They will not even look to see what it was because they will be distracted.
Magicmomentsandu.

Hint: Shooting enemies:
The best way to kill someone is to pull the trigger when your crosshairs are red.
joshua steele.

Hint: Shooting hidden enemies:
Some enemies hide in areas where you cannot shoot them. Throw a grenade at them and they will jump out of hiding. When they jump out, they will land on the ground on their stomachs. They will require a few seconds to get back up. Before they do, aim and shoot them or they will go back and hide again.
SVB1115.

Hint: Custom level names:
Note: This procedure involves editing a game file; create a backup copy of the file before proceeding. To change the names of levels, open the "title" file located in the "/english/pc/game" folder. Then, change the name of a desired title.
Sam "Azure" Doo.