After you destroy the white E.M.M.I., you can proceed through Artaria on your way to the next area.
Get a Missile Tank
Now that you have destroyed the E.M.M.I. in Artaria, you no longer have to worry about hiding from it. The E.M.M.I. Zone will turn green on the map to indicate that it is safe.
Look at the map and you should see an area where the wall is marked in blue. Go there and jump up against the blue wall while tilting the left control stick toward the blue wall, and you will grab onto it. Climb along it and it will lead you up to a door. Go through.
Jump up against the blue wall above the door, then jump upward while tilting the left control stick up to grab the blue ceiling. This will pull the ledge downward. Jump onto that ledge and go through the door up above.
Go to the right, then jump up onto the ledge on the right, and go through the door there. Kill the slug creature above you, then climb up the blue wall above you, then jump onto the ledge to the right and climb up the blue wall there. The door to the left can't be opened right now, so ignore it and climb up the blue wall above it. You will see a Missile Tank to the right. Shoot the wall between you and the missile tank until the wall is gone, then jump across to get the Missile Tank. Then jump onto the uppermost blue wall on the right and it will move downward, revealing an E.M.M.I. Zone Door. Go through it.
Go to the right and downward. Shoot the red thing in the wall to open a new path. You can optionally go through the door on the right to reach a save room. Afterward, leave the save room through the door on the left. Climb back up and go through the door on the right.
Go to the right through the tunnel while avoiding the enemies that shoot out of the ceiling, then slide through the gap on the right. Go through the door. Ignore the blue wall. There is a creature on the door to the right. If you get close to it, you can watch for it to flash, and perform a Melee Counter, then shoot it to kill it. It will drop a lot of health/ammo if you do this successfully. Afterward, open the door and go through.
There will be a cutscene, and then you will have to battle Corpius.
Corpius's face is vulnerable to missiles and charged shots. When it raises its stinger while pointing it downward, move away from the boss to avoid letting it drop the stinger on you. The stinger will get stuck in the floor for a few moments.
If it pulls its stinger backward, jump to avoid when it whips the stinger forward at you.
Corpius may sometimes spit out yellow blobs. You can shoot these with missiles or charged shots for a chance to get health/ammo.
After you hit it enough times, it will turn invisible except for a glowing orb in its tail. Hit that orb with missiles and/or charged shots while dodging its attacks as before.
Eventually, it will become visible again. You will be on the wrong side of the boss, and it will slam its tail down on you if you don't get to its other side, so slide under Corpius, then perform a Melee Counter when you see the flash. You will get some health and ammo for doing it correctly, and you will automatically aim. Immediately start shooting repeatedly (you will aim automatically during this phase) until the camera angle goes back to the usual side view.
As the battle continues, move away from Corpius if it comes toward you. Corpius may breathe toxic gas on to the floor. Go to the side of the room and grab the blue wall to avoid this.
Repeat these strategies until there is a cutscene where Corpius starts collapsing You don't need to do anything at this point; the battle will end. After the cutscene, you will get an Item Cube that grants you the Phantom Cloak ability. This adds an Aeion gauge beneath your health gauge. You can activate Phantom Cloak by pushing the right control stick like a button. When Phantom Cloak is active, the Aeion gauge will slowly deplete. It depletes much more quickly if you move or shoot while using Phantom Cloak. If you run out of Aeion, your health will deplete instead, but the Phantom Cloak will automatically deactivate when your energy reaches 1.
You can replenish Aeion by jumping, running, shooting, and performing other actions. You can only activate Phantom Cloak if your Aeion gauge is full.
Reach the Next Area
Go to the left and leave the boss room, and climb up the blue wall above you. At the top, activate Phantom Cloak and go left through the door. The sensors will not detect you, so the gate will stay open, so go through it. In the next room, go up and jump onto the blue wall. It will rise up to the top. From there, use Phantom Cloak to go through the door at the upper right of the area.
You will see lava through the windows in this area. Shoot the red thing at the top of the wall to open the path. Go to the right side of the room, then go downward from there. Go through the door at the bottom, then keep going to the right until you reach a save room. Go through the door on the right, then go to the right and use Phantom Cloak to go through the gate there.
Jump up and climb the blue wall on the left, then jump onto the platform at the top, then jump up to the blue wall and tilt the left control stick up to grab it. It will take you to the right side of the room. Shoot missiles at the flying enemies in the way so they won't knock you off. At the right side, go through the door.
Grab a blue wall but avoid the flames shooting out of the wall. At the top, kill the flying creature, ignore the door on the left, and jump up onto the platform and stand on the glowing panel to travel to the next area, Cataris.