Ecco the Dolphin: Defender of the Future Cheats

To totally bypass the giant crayfish boss, as soon as you enter the room he's in, dash straight down to the edge of the rock pile. You'll see a very small gap between a few of the rocks, keep dashing straight into it until you end up -under- the pile, then continue down the tunnel.

Go to the Powers of Levitation level. Once there, swim the large central building underwater and search around it until you find the Information Shard. From there, enter the central structure and cruise down the tunnel until you find an oval door near the bottom. Head through the passage which is split up by doors that dilate when you get near then so that you can pass through them. Ignore the side paths and just head down the tunnel to the chamber at the end. Inside is a clan member and an air producer in the center of the room. Turn and face the entrance and you'll see an oval section of wall to the left that's moving a bit with the current. Swim through it and you'll find a secret room--inside is a Stealth power-up. Grab it and head straight back, and you'll find a pair of yellow lights at the back of the room. Touch your nose to the right one and you'll enter the soccer room.