Uplink in the Navigation Room. Adam thinks the damage done to Sector 4 was purposeful, suggesting that the SA-X has high intelligence. Sector 4 housed a creature called Serris, which can move and attack at ultra-high speed. Adam shows you the location of Serris's breeding tank, and tells you that you've been authorized to kill it. He warns that the water in some places may be electrified by broken power nodes.
Sector 4 (AQA)
Exit left to the Save and Recharge rooms, and continue left to Sector 4. Take the platforms left and use the bottom left door, and continue left to the next room. Jump onto the ledge above and to the right, killing the Scizor above you, and jump to the upper ledge. Morph and bomb the block at the top, kill the Scizor on the rungs, and grab hold, pulling yourself to the far left. Drop below onto a block (the chains show you where it is). Jump from block to block to reach the door at the top left, and go through.
Be careful of all the Scizor along the walls and Skultera in the tanks. Jump up onto the ledge above, get in the tank and go through the door. Kill the Skultera-X, use the ladder, then press right at the top and jump over to the ledge. Save in the Save Room to the left, then back in the last room head right. Get rid of the Scizor in the way, get onto the small ladder, jump from there to the other ladder, then jump from there onto the platform and go through the door below. Your path is blocked, but grab the Energy Tank here, then head back.
Make your way back to the room with the small tanks filled with Skultera and the Scizor on the walls. Use the ladder to get out of the tank, then drop below from the ledge and start heading left and down to the bottom left door. Go through.
The water in here is electrified, so be careful. Shoot the big block above the door, then pull up into the tunnel and lay a bomb next to the long block blocking the rungs above. Grab onto the rungs and pull your way to the left. Jump up through the gap in the ceiling to a new room.
Take the ladder all the way up until you roll into a ball in a secret tunnel. Roll left to a new room. Kill all the Owtches and grab the Missile Tank to the left. Roll back through the tunnel to the last room.
There is nothing else you can do here, so just drop below and through the gap in the floor to the last room. Bomb the wall to the left to get through, and enter the door ahead. Don't go through the blue hatch (it leads to the Pump Control Unit; you'll be returning there later); instead, shoot the block above the right door. Climb up the ladder, then grab the rungs above and pull to the left. On the ledge to the left, shoot the ceiling to break it open, jump above and bomb the blue block to the right. Climb up, use the rungs above (there are Pit Blocks below), then on the next ledge shoot below you to break open the floor and fall below. Climb the ladder, shoot above you to open the way, then jump right from the ladder and go through the door to a Save Room.
You should save your game at this point, as Serris is up next. Once you've saved, shoot the cracked block in the right wall and roll through the tunnel, bombing your way through to a door. Go through.
You've reached the breeding tank, and you see Serris's remains. Go through the door to the right. Make your way up with the ladders, and drop down to the Living Door. You don't have a lot of room, and the water slows you down, so jump quickly if it's about to shoot out a membrane. Once the eye is destroyed, grab the red X, and go through the door.
Jump up onto the platform above the water and head right, standing on the less cracked-looking blocks. The more cracked ones will crumble, and Serris appears.
Serris's head is its vulnerable point, and can only be hurt with Missiles. You can stand on the platforms and attempt to shoot Serris as it winds around at a high speed (it can be very hard to see Serris in time to jump to avoid it) or you can stay in the water and watch the ground for a cloud of dirt to appear, indicating Serris's head is about to pop out there. (Staying on the platforms is probably best, due to how much slower you move in the water.) Whenever you hit Serris, it glows and becomes invulnerable for a while and winds around even faster than before. Luckily, Serris only takes a few hits before it becomes a Core-X. Kill it as usual, then absorb the Core-X to regain your Speed Booster ability.
Now, if you run for a few seconds, you'll start to run at a high speed. Certain special blocks (Boost Blocks, marked with a yellow arrow) can be broken if you run into them during a Speed Boost. Also, once you've Speed Boosted, if you crouch down you'll still be energized, and if you jump in that state you move in a straight line until you're stopped by a wall. This is a Shine Spark. You can break Boost Blocks from below and at angles when you do Shine Sparks. Once you've crouched and pressed A to jump, you will float up and can press left or right to jump in that direction, or press diagonally up to jump at an angle.
Sector 4 (AQA)
Jump up to the door at the upper right and go through. Get up on the platform and run to the right, then roll into a ball and bomb the wall to the left (you'll see that the blocks below are the special kind that break if you hit them during a Speed Boost). Go all the way left killing all the Owtches in the way, then from the far left wall run to the right until you Speed Boost and destroy those blocks. Fall down below.
Press left so when you fall through the Pit Blocks you don't land at the bottom. If you do, you'll have to Wall Jump back up. From the ledge you hopefully landed on, jump up as a ball and bomb the long block to get rid of it. Roll through the tunnel and bomb the winding block to the left to expose the ladder. Stay down below and bomb inside the little niche to reveal a Missile Tank. Once you grab it, climb the ladder and center yourself on it, and shoot two Missiles to the left. If you aimed right, two Missile Blocks will break open. Roll through the passage until you drop below. Drop down to a passage, then jump over the gap and stand on the small ledge. Jump up and shoot the wall to reveal a passage. Go through it to get a Missile Tank, then go back to where you were.
Drop down below to where there are a couple of Pit Blocks hidden in a blue ledge, and save in the Save Room to the right. Back outside, go to the far left and fall below. Make your way left from block to block and go through the door. In the room with the Scizor, and tanks with Skultera, use the bottom left door. Reveal the rungs as you did before, pull across them to the left, continue left and go through the door. Then go through the blue hatch straight ahead to the Pump Control Room. From the entrance to the Control Room, run to the left until you Speed Boost through some blocks and can reach the console. Stand on the pod to lower the water level.
Climb a little ways down the ladder, then jump right to reach a Missile Tank. As a ball, jump into the passage to the right, roll through and drop below, then take the platforms up, shoot the blocks above to break them open, jump above and exit right. Exit right again.
Roll through the narrow gap under the block, and fall down to the floor below. Kill all the Scizors here, then approach the left wall but don't touch the wires. Run right until you Speed Boost through some blocks. At the far right side of the next room, pull up above to reach a Missile Tank on the left. Pull up to the left and roll through to fall through a Pit Block. Exit to the left, stand by the wall to the left, and make a running start to the right, keep running and you'll break through some barriers in the next room; keep running and you'll get to the door. Go through.
You'll be locked in, and must kill the Scizor. Once it turns into an X, the X will become a Golden Scizor. Kill it with charged shots or Missiles. Once you beat it, the doors will unlock; exit right. Get to the top right door to reach the Recharge, Save, and Navigation Rooms.
Uplink in the Navigation room for your briefing from Adam. HQ has sent upgraded Missile data, but the Data Room in Sector 4 is locked with a Level 4 lock, and so can't be accessed. The Data Room in Sector 2 is also blocked by what appears to be deliberate activity by the SA-X. You are to find the Data Room in Sector 3 (PYR) to download the Missile data.
Exit right, take the elevator up, and head down to Sector 3.