When you are in the "password entry" screen, you can enter these "please" codes to reach the corresponding levels.
Password - Effect
PLEASEHH - City of Forever
PLEASEKK - Deep City
PLEASEOO - Final Fight
PLEASEEE - Ice Zone
PLEASEFF - Island Zone
PLEASEUU - Marble Sea
PLEASEWW - Open Ocean
PLEASEQQ - Origin Beach
PLEASEGG - Pteranadon Pond
PLEASEZZ - Ridge Water
PLEASEII - Undercaves
Invincibility
When the level name appears, hold A + Start until the level begins. When the game screen appears, unpause and you've got invincibility!
Music Off
To turn off the background music, pause the game and press A five times.
Options
While playing, move Ecco left and right and pause the game with Ecco facing you. Next, press Right, B, C, B, C, Down, C, Up. A menu will appear, offering you several options including level select, sound test, and invincibility.
Passwords
The Undercaves AAAAAAAA
The Vents AANNAANN
The Lagoon NDRBRIKR
Ridge Water HYAUGFLV
Open Ocean FNCQWBMT
Ice Zone DWFFZBMV
Hard Water ANANANAN
Cold Water MCLFRQLW
Jurassic Beach MDEBRCBO
Pteranodon Pond JNXFRCBS
Origin Beach AAAANNNN
Island Zone NNNNAAAA
Deep Water EILQOQLC
The Marble Sea XAKUQQLS
The Library FDGXQQLC
Deep City AANNNNAA
City of Forever DETSWCIY
Trilobite Circle DETSWCIY
Dark Water NNAANNAA
Deep Water 2 EQAAKNLC
City of Forever 2 ZBPIGPLD
The Tube KUVEKMLK
The Machine NNNNNNNN
The Last Fight KNLMLMLC
Super Sonar
For lethal sonar, enter any Unlimited Air code, then press A + B while playing. Your sonar will look the same, but will kill all enemies it detects.
Unlimited Air
Here are some passwords for unlimited air. For unlimited air in a new game, enter "LIFEFISH" as your password.
The Undercaves LEVELSCT
The Lagoon SHARKFIN
Open Ocean KHDBVRIS
Ice Zone XRGQXRIX
Hard Water MAGLXRLM
Cold Water LNXHXRLB
Island Zone DVJLURIC
Deep Water OEWSURLC
The Tube FIVEPODS
The Machine ECCOFMLY