By the intended route, the Sewers level is a 6–7 minute level, one of the longest in the game. However, the interconnected layout of the level makes it vulnerable to exploits; in fact, most of the level can be skipped, and an optimal playthrough of the Sewers can clock in under 90 seconds.
OVERWORLD In the overworld, make sure your active Morph power is set to Vault, and cutscene-override past the dialogue with Doppler and Amelia.
ROOM 1 — FOYER Once you enter, head immediately north to the edge of the stairs, and then west over the low platform. You will get hit by the closest robot in doing so; this is intentional, and allows us to enter the other robot's line of sight at a more opportune moment. Proceed around the pillar-thing on its north side, and once the second robot sees you (identified by the audio cue of its 'grunt'), move up to the west wall, adjacent to the platform on which Morph Bright is found.
Start your Vault when the robot reaches the tile to your immediate east, and you should successfully damage boost off its head. It is possible to cutscene-override through the Morph Bright text box, but the timing is very precise; if not, just use the Start button to skip the text. Once you have Morph Bright, proceed down the stairs and into the next room.
ROOM 2 — SEWER ENTRANCE This is a relatively simple room; mostly, you just need to cross the room to the eastern door.
Make sure not to walk on the tile immediately at the bottom of the stairs, or it will trigger a cutscene; it's possible to clear the tile by jumping, but using Morph Leap is more reliable. If you maintain a consistent walking pace, you can walk over the first steam vent without getting hurt; however, you will need to jump over the later steam vents.
At some point during the steam vent section, make sure to switch over to Morph Strength.
ROOM 3 — CRATE ROOM Here's where it gets interesting.
When you enter, the crate will be immediately to your north. Don't grab a torch yet. Get on the east side of the crate and begin pulling it until you're lined up with the torch over to the north; step over to the torch to illuminate the room, and switch to Morph Vault. Vault over the crate, switch back to Strength, and begin pushing the crate when you land on the opposite side.
(NOTE: You don't actually have to illuminate the room, and not doing so could save a minute amount of time. However, lining up the crate jump is tricky enough that I'm more comfortable being able to see what I'm doing.)
Push the crate all the way into the sewage. You only have about 3 seconds before it explodes, so make sure to do this next part quickly:
Switch over to Morph Leap and jump onto the top of the crate. Get to the southwest corner of the crate— potentially even edgewalking over the south side— and Leap across the sewage. You will land on the edge of a switch tile on the east side of the room. Get onto terra firma and proceed south across the bridge of lifts, avoid the Spike Slug, and exit through the south door. At any point during this part of the room, switch over to Morph Vault.
ROOM 4 — THE SPLIT HALLWAY Once you enter, step east to pick up the torch to illuminate the room. Avoid the Spike Slug and Vault up onto the east side of the elevated platform; switch over to Morph Leap as you walk westward across the platform, and at the western extremity, Leap across the sewage. You will land on a destructible platform; jump onto the western side of the hallway, avoid the Spike Slug, and switch over to Morph Vault. Exit to the north.
ROOM 5 — CRATE ROOM, PART 2 You're now in the southwest side of the Crate Room. Skip the torch; walk two tiles north, then Vault up onto the platform. After one tile, jump across the gap; your intended landing tile has a gem on it, making it easy to get your bearings. Then jump off the west side of the platform, switch to Morph Leap, and exit through the western door.
ROOM 6 — SEWER ENTRANCE, PART 2 Skip the torch again here. Walk up to the edge of the platform (where there are footprints visible) and jump up. Leap across a field of spikes, then jump over the row of fire vents. (Getting hit by the fire vents usually screws up your momentum, so wait until you can avoid them.) Leap across another field of spikes afterward, then jump over a ditch.
You're now walking across two tiles before your next jump, so switch over to Morph Vault now. After walking two tiles, jump over a row of spikes, and then Vault up to the platform with Doppler's suit part. DO NOT cutscene-override through the resulting dialogue; you will either lose time or softlock.
