For all weapons, type HUIBON while playing.

At the Password screen, type in COMMANDO.

On modern wars 2 the very first thing you see will be a dog. Do not kill as him he shows you tips by digging in the ground. When he stops moving kick him to keep him going. Try not to kill him because he bites people that hit you.

To heal yourself, type VONLUX while playing.

Level          Easy       Normal     Hard
Roman          YPTERFGZ   QJSLVABL   SOIOLGNK
Japan          NKTOLVIF   KAYAGEAF   TFJSVJMC
Middle Age     VMXYICCB   MZFSPQDD   XFYAMXIE
Conquistadors  FDQLUGGC   AVMJFGGU   ZOVASAIV
Wild West      ZREHQFIR   EVBSVTCV   BODSGWLW
Modern Wars    FBTAWPFC   YLHHGXBO   VEJHMQKO
Future         EFBYQHME   ALPYPJFO   ZEYPCEHQ
Beyond Time    CWFLWYHC   YBULVABN   HMFDLGNN

For auto-reload, type in OTOREL. You will hear a sound. Very helpful in later stages.

Type in Venruf to stop the virus, there will be a sound if you do it right. This is very helpful for harder modes

In Level 2, in Medieval Times, when you face the two knights at once, get them close together and trick one of them to hit the other. They will start fighting each other and then you will only have to face one knight instead of two.