In Act 3, you are in the Locust tunnels and must plant the Resonater in the building behind a lava filled lake. There are rocks on top of the lava, allowing you to walk across; however, it is not that easy. About one third of the way across an intermission sequence starts, with a giant spider creature, the Corpser. All you need for this battle is a shotgun and machine gun. This will be a fairly long range fight. It is an easy fight but the Wretches that come from everywhere complicate it. When the Corpser raises all his legs and slams them down, your teammate will probably yell "Wretches!". This is your cue to take out a shotgun or use your machine gun. At the beginning you should have a point of interest on the stomach, which is your cue to shoot it. You can always get a shot on it, even when the Corpser shields itself; or you can wait until it tries an attack then shoot its stomach. After that there will be another point of interest, which is in its mouth. When you shoot the stomach it will cringe and its mouth will open as it screams. Then, shoot it in the mouth. While you are doing this, watch out for the Corpser's Ground Pound. It not only brings Wretches (watch the ceiling), but also takes away part of the arena in the back. If your character dies in the back he might be lost. Your ammo cases may also be lost. Keep repeating the process of shooting the stomach and the mouth until the Corpser backs up as far as it. It can no longer be hurt. There will now be a point of interest around the smashable latches. There are two of them. Shoot both of the latches so that they pop, and the platform that the Corpser is on will be sent into the lava.