Gears of War 2 Guide - Act 2: Denizens
Chapter 3: Strange Revelations
Start down the path and eventually you will reach the entrance to a Locust stronghold. Be sure to pick up the Longshot that's on the ground just before the steps. Immediately take cover behind one of the pieces of railing to avoid taking fire. Look up in the left corner of the cave ceiling for a glowing fruit, and shoot it down to lure the Rock Worm into the area. There are some Tickers in this area as well, so don't let one get too close. When the Rock Worm is in view, hop over the railing and take cover somewhere along it.
If you have one or more Frag Grenades, toss them into the two sectioned-off areas on either side of the entrance to take out the grubs hiding there. Eventually the Kantus will come through the front door sided by a group of Wretches. Empty your Lancer into the Kantus until he falls, but divert your attention to the Wretches if they get too close. The Kantus was carrying a Gorgon Pistol, so be sure to pick it up before moving on.
Collectible (1/1): Enter the stronghold once the Kantus has been dealt with and make a hard right. The collectible (Locust Emblem) is on the ground near the ammo box here.
Once you have the collectible, start following your allies deeper into the stronghold. You'll come to a ladder, and you then must choose between the Left path or the Right path. You won't miss anything by choosing one path over the other, but for the sake of following this walkthrough, choose the Right path.
Right Path: Grab the ammo box and Frag Grenades in front of you and then immediately take cover behind the Rock Worm. If you have a Longshot with you, this'll be a piece of cake. It's your job to take out the gunners in the Troika nest here. Dom will shoot down a piece of hanging fruit to lure the Rock Worm further into the area, so follow along so you don't lose your cover. Pick off both Troika gunners with headshots from behind the safety of the Rock Worm. If you are out of Longshot ammo, lob a Frag Grenade or two through the windows instead.
Afterwards, enter the building and pull the lever right by the entrance to open the door next to it. Head through the open door, go down the path, climb up the ladder, and take out the Troika gunner behind the sandbags. Toss a Frag Grenade up there if you can spare one. Continue along the path until you reach some sandbags overlooking another Troika emplacement. Take cover behind the sandbags, kill the gunner, and then take care of the Kantus below as well.
Climb down the steps, hop on the Troika, and use it to eliminate the Drones below. A Boomer and some more Drones will enter through the large door on the right, so turn there and gun them down with the Troika.