Sonic's Secrets: Ecco the Dolphin CD.
Cheat Menu.

You can call up a cheat menu menu at any time during a game.

Move Ecco left and right, and press start to pause the game whilst Ecco is facing you, as shown on the right.

Next, press:

Right, B, C, B, C, Down, C, Up.

A menu called "The Dolphin" will appear, offering you several options including level select, sound test, and invincibility as shown on the right.
Passwords.

Use the following passwords to jump to any point in the game.

Level Password
 The Undercaves  GMRIQDCM
 The Vents  IUEINLDP
 The Lagoon  GRTJZYJF
 Ridge Water  OVDJDSLB
 Open Ocean  GMYMDSLI
 Ice Zone  GMBRHSLU
 Hard Water  UKZFHSLS
 Cold Water  SYQJHSLZ
 Open Ocean 2  CCVFFSLM
 Island Zone  ALZBESLS
 Deep Water  IHPFDSLP
 Volcanic Reef  ADLYESLT
 Ship Grave Sea  INWUGSLU
 Wreck Trap  WJHQGSLL
 Sea of Silence  IZSXGSLF

Level Password
 Deep Gate  AKNBHSLI
 Marble Sea  QSOMFSLQ
 The Library  WBTXFSLV
 Deep City  UNIQFSLN
 City of Forever  WADUFSLB
 Jurassic Beach  ONNBJPLY
 Pteranodon Pond  WPVXIPLL
 Origin Beach  AQZIJPLG
 Trilobite Circle  GKGFJPLK
 Dark Water  GZIUKPLR
 Deep Water 2  GAAGDPLP
 City of Forever  YLQQZNLM
 The Tube  MNEYELLB
 The Machine  SKZNELLO
 The Last Fight  KANZFLLX