When you are fighting alongside Alyx later in the game, at one point you will encounter a door where she tells you to go on without her, while she heads up to the communications room to unlock doors for you. Push her into the corner left of the door, then run in and watch it close behind you. As the next area is loading, she will appear next to you. This clone does not talk, and is not always there; however, later when both of you fight a group of soldiers, there are two of them.
Debug mode
Press Start, Up(6), Down, Start, Up(3), Down during game play.
Flip jeep
When you get the jeep, use turbo towards a wall, then press Y to get out before you hit the wall. If done correctly, when the jeep flips you will also flip. Note: You may also get hurt.
Get on top of stairwell in Anticitizen One
After Dog attacks the dropship and it drives off, go to the bent down fence and jump over it. Walk down a few steps and on your right will be an open door. Go in it and to your left you will see a stairwell blocked by a couch and debris that cannot be moved. Crouch jump over the couch and go up the stairwell. Bring a box with you so that you can put it on the ground in front of you, then jump on top of it and make longer jumps.
Getting past turrets and other dangerous enemies
When you need to run a long way and you have some objects with you (for example, a non-explosive barrel), if you have the gravity gun, use it as cover and run (while facing the enemy) to the other side. Then if possible, shoot the barrel at the enemy. Note: Make sure there are no more that one enemy while doing this. Also, make sure that the object is indestructible, and most importantly, look at the enemy and see if you can kill it with one shot.
Gravity Gun
Have the SMG equipped, then press Down, Up(2), Down, L, R, X, B, A while playing a game. Note: This code cannot be enabled if the "Organic Gravity Gun" code is activated.
Nove Prospect: Death by looking at wall
Get to the end of Nove Prospect where the wall comes in and you need to get to higher grounds by the fire. At the location where a Head Crab comes at you, turn to face the wall and look for a opening go through. You will die.
Organic Gravity Gun
Have the Gravity Gun equipped, then press L, Black, R, White, Up, Down, Y, X, B, A while playing a game. Note: This code cannot be enabled with the "Inorganic Gravity Gun" code activated.
Punting objects
Pick up an item without using the Gravity Gun. Drop it until it leaves the bottom part of the screen, then pick it back up and throw it as fast as possible. If done correctly, it will appear as if you are kicking the object. This is especially fun to do with the toy doll at the beginning of the game. Note: This works best with lighter objects.
Spawn medpak
While playing a game, press Up, Up, Down, Down, Left, Right, Left, Right, B, A to spawn a medpak that will restore 25 points of health.
The ultimate shield
When you are getting attacked by the small evil things what jump on you.You can shield them off by using a brick!Its so fun u can block them off and never get hit.Now you've got yourself a trusty brick companion.
