Act 2: C6 - Intestinal Fortitude
Yep, you are inside the Riftworm. As soon as you start, go left and up for a magazine. Move along, and of course you fall into that stuff, then move up to the digestive teeth; didn't we all learn about digestive teeth in biology, the kind that digest Mario? Roadie run (hold A if you didn't know) the first two, then slide to the left of the third to run a bit easier. For the next set of teeth, just roadie run and don't stop or get caught because if you stand up you die.
Ammo to the left, then move along once most of your team is with you. The next teeth require patience for the vertical ones, but you must run through the horizontal set. Up ahead will be some new creatures, so lancer them and then move up for another sad scene. Then run up and keep following the path to a valve. Shoot the opening and then run through. Avoid the barbs and swing around to some tissue and cut it open.
*NOTE: Watch out for the things that stick up out of the ground and the acid that's hard to see.*
Run through and shoot a second valve. Run along the water and at what seems like a dead-end, look up to the right and shoot down the car to make a path. Then run to the final membrane and cut it to be our of harm's way.
In the stomach, go up to the left and shoot the tip of the acid nozzle, then run through. Then two, and for the rest you just need to get close, shoot them one at a time, and run through. Ammo and then you hit some toxic intestines. Just move straight, avoiding the black smoke paths, then take a left toward a red area and keep moving to a membrane to get out before dying.
Then just follow the path to the heart. Cut two arteries on the side, then a path opens up. A few crawlers along the way, which your buddies don't seem too thrilled to help you kill unless they go after them. Ammo on the right and then cut a membrane to the second heart. Go up the ramp on the left and start cutting. A path opens up to the next heart.
Through the membrane you have a large chamber. Some ammo by the body (how did he get here?) then go left to fight a few crawlers, and more will appear on the right that your buddies handle. Then make your way up to the left of the heart and quickly cut the two arteries, then hurry to the right side, maybe ignore the three crawlers or quickly attack them, and hurry to cut the last two bloodlines before you drown in blood. That's it.