If you know what to do, this can be one of the most satisfying boss battles you’ll ever have. Keep the following tidbits in mind before beginning. If your battle meter hits zero, you’ll have to start the entire train mission over, so be careful and prepared. It’s also extremely helpful if you have a real-life person to help you co-op against this boss. Anyone with two hands and penchant for pressing ‘B’ will do.
As soon as the level starts, pick up the shell in front of you and run straight through the hall and between the two orange T-ENG rechargers. At the top of the ramp, turn around and grapple up to the top of the train car. Lug the shell over to the left side of the cannon near the middle and press ‘Y’ to load the cannon. The shell will move up to the middle stage of firing. Walk up the cannon to find the energize station. This is optional, but increases the cannon’s fire rate. You can turn the cannon two ways. You can jump in the gunner’s seat and move it slowly yet manually, or you can use the rotation stations on each side of the cannon for a quick ninety degree turn. The Akrid is vulnerable when it pulls up alongside the train exposing the nodes along its back.
Once in the gunner’s seat, press fire to load a shell into the final stage. Blast away at each of the Akrid’s nodes: once to remove the shell and again to destroy the glowing goo underneath. Your real-life teammates should be loading shells, energizing them, and turning the cannon for you. Your AI teammates will only bring shells upstairs and occasionally load them, but the rest is up to you.
An alternative way to damage the Akrid’s nodes is to use the mounted turrets just down the hall from the coolant stations. When the Akrid surfaces and opens its mouth, it is preparing to bite down on the train and take half your hit points. Take cover inside or against a ledge to avoid being knocked off. If the cannon is ready to fire and happens to be pointing in the right direction, you can fire down the Akrid’s throat to stop it from attacking.
If you’re the cannon’s blue life meter falls below the halfway point, run back inside and use the coolant stations to refill the meter.
Once all nodes are destroyed, point the cannon forward and fire the cannon down the Akrid’s open throat to put it down for good.