Cheatmode:
 Load game with the hl.exe -dev -console -game gearbox command
 line. Press ~ during game play and enter one of the following
 console commands to activate the corresponding cheat function. 
 
 Effect Code 
 -----------------------------------
 All weapons and ammunition - impulse 101  
 God mode - /god 
 No clipping and flight modes - /noclip  
 Level select - /map   
 Spawn item - /give   
 Enemies ignore you - /notarget
 
 Level select:
 -------------
 Map Names for /map above
 of1a1
 of1a2
 of1a3
 of1a4
 of1a4b
 of1a5
 of1a5b
 of1a6
 of2a1
 of2a1b
 of2a2
 of2a3
 of2a4
 of2a5
 of2a6
 of3a1
 of3a1b
 of3a2
 of3a3
 of3a4
 of3a5
 of3a6
 of4a1
 of4a2
 of4a3
 of4a4
 of4a5
 of5a1
 of5a2
 of5a3
 of5a4
 of5a5
 of6a1
 of6a2
 of6a3
 of6a4
 of6a4b
 of6a5
 of7a0
 
 Weapon select:
 --------------
 /GIVE WEAPON_X - give weapon X, where X equals:
 
 GRAPPLE
 KNIFE
 PIPEWRENCH
 EAGLE
 M249
 SNIPERRIFLE
 DISPLACER
 SHOCKRIFLE
 SPORELAUNCHER 
 
 Get a gun at the beginning of the level:
 At the beginning of the level where you reach the security 
 guard, find a chair. It is easily moved. Move it to the door 
 that he will open for you, and get him to open it. 
 Slide the chair in between the doors, and it will not close. 
 This may take a few tries. Go out, take the crowbar, charge 
 it up until you reach the same security guard, and hit him 
 until he explodes. Then, get his pistol with the laser sight 
 and continue the game.
 
 Spawn Grunts:
 Enable cheat mode, then use the impulse 76 code to 
 activate the Grunt-O-Matic. A message to start a new 
 game in order for it to work will appear. If you want 
 to continue where you currently are, just quicksave, 
 then quickload the game. Once you have quickloaded, type 
 in the code again to spawn a Grunt. Note: You must have 
 the nocliping code on before you spawn the grunt because 
 he will be spawned close to you. If this is not done, a 
 message stating that the monster spawned is stuck in a 
 wall may appear and the game will end. Do not spawn the 
 Grunt in a closed position or the same message will appear. 
 The Grunt you spawn will see you as a hostile. To have more 
 fun, use the /notarget code and spawn a number of grunts to 
 do your alien hunting. The Grunts you spawn will look like 
 the Grunts from the original Half-Life. 
 
 Hidden audio:
 Approach the Boss of Opposing Force to hear backwards 
 audio composed of the phrase "To win the game you must 
 kill me Randy Pitchford" when played correctly. 
 Randy Pitchford is the leader of the development 
 team at Gearbox Software. 
 
 Original levels:
 You can play all the Half-Life levels that Gordon Freeman went 
 through as Adrion Shepard, but in the lab none of the scientists 
 will talk to you.
 
 Hints: 
 Save your ammo! If you can take out an enemy with the 
 wrench, use it instead of unloading a clip.
 
 Maintain control of the medic; if you "release" him, other 
 grunts will yell for medical assistance and they'll take 
 the medic's supply of shots, leaving you with nothing.
 
 You can only use the Barnacle on organic materials--these 
 are usually green, with small lumps. Latch onto them and 

Third Person:
Firstly, activate the console and bring it up during gameplay. Then, type 
in /thirdperson and press enter. You can now play Opposing Force in the third 
person.

Hidden Suicide Technique!:
At the part where you see Gordon Freeman jumping in the portal to Xen, notice 
that the portal is still open for about 5 or 10 seconds. When you open the door, 
quickly run after Freeman and jump into the portal. Instead of landing on a 
platform, you will just fall and then you will see a short sequence showing how you 
died.