While on the level, kill the first three little opponents. After that, two Lokis/Hellbringers and one Mad Cat/Timber Wolf will approach you. Take off one of the three mech's leg so it falls over and kill the other two. Now move directly opposite of the city so that you are heading to the mountains. There should be a couple passes that let you to the top. You are now at the edge of the map and can drop down. You will take some leg damage, but it is worth it. You cannot get back up, but you can now shoot your enemies from underground. They cannot hurt you, but you can hurt them.
When an enemy mech is on the other side of a wall, ram into the wall and zoom in. You can see and shoot through the wall. Note: This trick works with mountains and other walls that can not be destroyed.
Note: The v1.1 patch is required. To salvage mechs almost totally intact, enable the "Invincibility" and "Jump Jets" codes. Then, jump up and land on top of them until they die in a "death from above" maneuver.
Activate the following cheats by entering the corresponding codes while holding CTRL + ALT + SHIFT:
CHEAT FUNCTION - CHEAT CODE Toggle invincibility - su Toggle unlimited ammo - is Toggle heat tracking - oo Nuke current target - it Destroy current target - re or nu Jump jets - in Unlimited jump jet juice - cr End mission successfully - li Free-eye mode - be