Enter this code at the options menu. You should be taken to a new section of the options menu that'll let have access to any level, choose how much health and lives you have and lets you choose which powerup weapon to start with. Only downside is you can't see the good ending if you use it.
Hold Up while turning on the game. Keep holding Up until you see Knuckles grab the third Chaos Emerald during the Intro. Press Start when Knuckles grabs the third Chaos Emerald. You'll hear a chime if done correctly.
Level Select
At the title screen, Press Up or Down to access Sound Test and Time Attack
Sonic CD - Level Select, Sound Test, Sonic Team's Best Times
At the Title Screen when it says "START GAME" enter the fallowing codes. You MUST Tap, as in the D-pad can Not be held down for more then 1 MilliSecond, for each button press. You will Automaticly be sent to the fallowing screen for the code you entered.
Note that the Level Select is used to only Practice the game and that you will be sent back to the Title Screen when you finish a level or warp.
Select Sonic as your character in single player, and fight your way through the 8 battles without losing a single round (that means no losing the match and starting over from round 1). Defeat Metal Sonic in stage 9 in round 1. In round 2, activate Hyper mode (back+punch+kick) and Sonic will transform into Super Sonic, making him invulnerable for the rest of the game.
If you have Radiant Emerald and Super Sonic unlocked, just select Super Sonic and play as him in Radiant Emerald to hear him theme song, Super Sonic Racer, instead of Diamond in The Sky.
When examining an illustration in the Museum, press X. You should hear a sound. A slideshow will start featuring all the pictures you've unlocked so far. It'll skip over:
Non-pictures (videos, demos, etc.) Pictures still marked as NEW Pictures you haven't unlocked
On the Sonic Chaos demo to play the full version without beating the game or losing all of your lives, Insert a second controller into slot two and press start. The clock will reset, and a second screen wil appear with the full version on it!(Note: The second player's screen will not have sound)
When you start Vectorman, you can move him. Do so and place him under the SEGA logo. Shoot the logo exactly 24 times, then jump up Vectorman's head bonks the logo 12 times. The logo will disapear, and the letters will keep falling from the top of the screen. Try to catch the letters. If you get 100-109, you can skip to level five, and if you catch 110 or more, you can skip to level ten!
These should start up after playing 3 days in a row. After that, simply play each game every day to continue unlocking them. They'll appear in the musem menu. Also note that if you defeat the boss fast enough to get through the ending, you can use the remaining time playing the FULL version of the game!
Unlockable
How to Unlock
Dr. Robotnik's Mean Bean Machine (and Game Gear) Final Puzzle Demos
Play for 7 days
Sonic 1 Final Boss Demo, Sonic 1 Game Gear Final Boss Demo
Play for 3 days straight
Sonic 1, 2, 3, & Knuckles Good Ending Demos
Play for 8 days
Sonic 2 Final Boss Demo, Sonic Laberynth Final Boss Demo
Play for 4 days
Sonic 3 Final Boss Demo, Sonic Drift Final Race Demo
Play for 5 days
Sonic 3D Blast Final Boss Demo, Sonic Blast Final Boss Demo
Make sure that Vectorman 1 and 2 are already unlocked on your game, and that total play time is 12 hours. After fulfilling the conditions you will have to exit the game select menu and re-enter for the game to register the game as unlocked.
Unlockable
How to Unlock
Bare Knuckle
Play Bonanza Bros. at least once, play any game(s) at least 30 times.
Bare Knuckle 2
Play Bare Knuckle at least once, play any game(s) at least 50 times.
Bare Knuckle 3
Play Bare Knuckle 2 at least once, play any game(s) at least 70 times.
Bonanza Bros.
Play Vectorman 2 at least once, play any game(s) at least 20 times.
To unlock the "Hints" text for each game, open a game and keep it open for three hours. You don't have to play the game, just let it run. After three hours, exit out, and when you re-enter the game or check the Hints menu in the Extra area, the hints for that game it will be available.
By achieving low times in Time Attack mode on Sonic CD, you can unlock new modes. Visual mode and Play Music will both appear on the Sonic CD main menu. Time Attack in Special Stages appears in Time Attack mode.
Unlockable
How to Unlock
Play Music
Get a total time of 37' 27" 57 or less
Time Attack in Special Stages
Get a total time of 30' 21" 05 or less. Then press left when on the Time Attack screen.
You can unlock certain pictures in the museum by veiwing other pictures in a sequence. You must unlock the pictures in the sequence before you can perform these tasks. After veiwing the pictures, you will hear an odd sound to confirm that you did it correctly. Exit and then museum renter the musuem. The appropriate picture will be unlocked.
Unlockable
How to Unlock
Museum picture 200
Select pictures 12, 23, 54, 10, 22, 25, 39, and 56 in that order.
Picture 160
Veiw pictures 146, 145, 144, 142, and 143 in that order.
Picture 180
Veiw pictures 162, 163, 164, 166, 170, 172, 174, and 178 in that order.
Picture 220
Veiw pictures 18, 106, 118, 136, 137, 138, 139, and 140 in that order.
Picture 260
Veiw pictures5, 4, 9, 8, 3, 6, 7, and 2 in that order.