Oil Field - Drilling Facilities
After escaping as the oil field explodes, Captain Josh Stone will take you towards Irving via boat. At the beginning of this cutscene, you will see that the Majini are pursuing you. After the cutscene, there will be two boats on your tail. Pick the Majini off with any gun. Using a sniper rifle and turning around, you will see four large oil tanks on top of the bridge; shoot them, and you will instantly dispatch any Majini. Keep your sniper rifle ready and shoot the oil barrel on the wooden bridge and next to a crossbow-wielding Majini. After this, there will be another Majini on your left and another barrel - shoot it. Zoom out and you will see two more Majini on the bridge; again, snipe the oil tanks next to them. Once you have passed them, you will end up in a base with a door blocking your exit. Climb up and take any path - left or right - but make sure to dispatch the Majini! You will find oil tanks on the top corners of the base. Before going into the boat, find the BSAA emblem located at the bottom of the door; there will be a hint of silver showing. Once you have opened the door, get back into the boat.
Once on the boat, shoot the oil barrels and remember to duck under the pipe. As you proceed, there will be another pipe and more oil tanks. After these two pipes, you will enter yet another, larger base and you will be blocked by yet another door. There will be two Gatling Guns after you climb up and face left and look up. Take out the Majini who are using the chaingun. Note that if you head right through the door fast enough, you can avoid fighting the chaingun operators. Pull the levers to open the door. Explore the place and you will find a Benelli M3 shotgun go on the opposite side of the boat and running away from the lever side continue straight until the bridge and you will find a pontoon path leading to the M3 shotgun. Return to the boat and you will travel towards Irving's ship, initiating another cutscene:
Chris and Sheva dispatch the ship's chaingun-wielding Majini guards, and go on the ship while Captain Josh Stone retreats from Irving. After complaining that everyone looks down upon him, Irving has a flashback with the bird-masked woman giving a syringe containing a master Plagas to him; as Chris and Sheva look on, he injects himself with the syringe and rapidly mutates. Using his new tentacles to spring into the water, he disappears beneath the surface for several seconds, then resurfaces as the core of a gigantic monstrosity.
This boss can be can be extremely annoying. Irving will first have tentacles flailing about on either the left or the right side of the ship. Use any weapon to shoot the tentacles, but it is better to use the Gatling Gun or the Rocket Launcher near the front of the ship. The tentacles will have a black mark near the middle; shoot that, and you will destroy the tentacle, but you need to destroy more to attract Irving to the surface. Be careful if you are using the Chain Gun against Irving's tentacles as you will have to dodge the attacks and get off the Gatling Gun at the same time. After attracting him to the surface, shoot the weak spot located at the head of the boss; it will attract his attention, and you will have to dodge its bite. Always remember to react to the botton attempt first, failing to react them often means instant death. Repeat this process until another cutscene is shown, wherein Irving himself reveals himself at the back of the ship and uses his tentacles to grab hold of it. Go to the back of the ship and shoot Irving with the Chain Gun; he will attempt to bite you, so dodge and repeat this process until you kill him.
A cutscene concluding the chapter will show Irving revealing more of the plot with his dying breath and promising that all the answers Chris sought were 'in the cave.