Act 5: Chapter 2 - Train Wreck
As you get on the train, you are immediately bombarded with many waves of Drones (about 12 in total) along with about 5 Theron Guards mixed in.
Once you reach a cabin with a door, you will receive a message from Anya about Nemacysts being located on the radar. Proceed to open the door with the green door button.
Eliminate the Berzerker Threat
As you open the door, you find it's stuck. So you have Jack open it for you, but as Jack starts to open it you are attacked by a Berzerker. Because of the Nemacyst clouding the skies, there is no way to use The Hammer of Dawn. You must find another way to dispose of it.
Lure it to one of the end train cars, back where you started the level. Then run back and find a car release button to dispose of the Berzerker and all the trailing train cars. Or, as an alternate method, you can lure her near the large fuel tank and toss a grenade near it. Just be sure to get off the train section the tank is on on because it will also release them.
Fight through the next few train cars, there will be plenty of Drones and Theron Guards along with a few Reavers flying by the side of the train cars trying to take you out.
Get to the Chain Gun
Clear out a few Drones in the next train car, and then you'll find a ladder past a door that you need to use a button to open. Climb it and get in the Troika mounted up top.
Clear out the Attacking Reavers
Find the ladder and go up the chain guns on the roof to clear out about 20-30 Reavers.
Keep the Train From Stopping
Anya calls to inform you that four cars ahead Wretches are cutting the power to the train. Fight your way through the next four cars through a few waves of Wretches and Dark Wretches, along with a few Reavers and Theron Guards. Be careful a few spots the enemies will pour out of the ceiling.
Once you reach the train car where the Wretches are eating through the power, you are given thirty seconds to reach the train car past the ones with the Wretches so you can disconnect it and keep the train moving.
Act 5: Chapter 3 - Pale Horse
You reach a final empty train car filled with ammo before the big end battle. I'd stock up if I were you. I recommend the Longshot and either the Gnasher (if you have it already) or the Lancer.
Kill RAAM
Stick behind the cover to avoid General RAAM's Kryll shield. Take shots at him to clear the Kryll shield and then continue to shoot at RAAM with whatever weapons you have. Repeat this over and over, while also avoiding any flying Kryll once the shields are dropped.
Depending on your difficulty level will depend on how aggressive General RAAM is towards you. On Casual he will usually stay on the other end of the train car and shoot at you from there, and will only occasionally charge you. But we found that on Hardcore he will approach you and Dom right away instead of staying back, forcing you to run and find more cover. Doing so exposes you to Kryll attack.