Ecco The Dolphin: Defender Of The Future cheats and cheat codes for Dreamcast

Full pause screen
Pause the game and press X + Y.

Unlock Dolphin soccer mini game.
There is a soccer ball on Powers Of Levitation level in the room 
where the clan General is located. Pick up, after jump to to the 
level selection screen. You will see a Dolphin soccer game option.

The not-so-silent sea:
In the Sea of Silence, if you press pause after press pause 
again, you will hear music instead of silence.

Active map (sonar)
Hold X while playing for a long time. 
Press X again to return to normal.