Press ' during game play in single-player mode to display the chat window. Activate the following cheats by entering the corresponding codes:

CHEAT FUNCTION - CHEAT CODE
2D players - turnpunchkick
Large torsos when breathing - 1-900
Very big heads - meganoggin
Big heads on all characters - bignoggin
Full ammo, refill items - 5fingerdiscount
Toggle victory conditions - explore
Disable AI - nobrainer
Stumpy characters - stumpy
God mode for selected person - avatargod
God mode for team - teamgod
Flatulent walking - silentbutdeadly or fastactionresponseteam
Large feet and hands - clodhopper
Invisibility - theshadowknows
Team invisibility - teamshadow
Wound yourself - wound
Kill yourself - death
Activate debug keys1 - debugkeys

NOTE 1: Once this code is active, the features in the "Debug commands" section below may be used.

Enable the "Activate debug keys" code and press F10 to enter debug mode. Activate the following cheats by pressing the corresponding keys:

EFFECT - KEY
Screenshot - F2
Enemy view - F6
Suicide - F7 or F8
Return to normal view - F9
Exit debug mode - F10
Level skip - F12
Adjust lighting - or }
Toggle AI - A
Third person views - V or B
Adjust elevation - Comma, Period, o

During a mission and some of your fellow operatives are killed, continue to complete the mission. When starting a new mission and the screen that asks if you want a default plan, do not select "Yes". Instead, click "No" and go on. When you reach the character selection screen, go down to the bottom right corner and you should see the "Save Plan" and "Load Plan" options. Click on "Load Plan" and select the one that reads "m**", where * is a number that corresponds to the mission (for example, m1, m2, m3, etc.). Look at the characters in the box that contains the ones selected for the mission. If you see one of the dead operatives in that box, do not remove him or her -- just begin the mission. After this, you should have that operative with you alive and well. 

On certain levels, there are drop-offs with ladders leading down to a lower level. If you have a teammate with you, face the hole, and get him in front of you. Then, push him in. You will see him try to get back up, or take the long way back, and eventually get back to you.