Sonic 3D:

Level select:
Press B, A, Right, A, C, Up, Down, A, Start when the phrase "Press Start" appears on the opening screen. The level selection screen will be displayed when game play begins.

Level skip:
Enable the "Level select" code. Pause game play and press A to jump to the next level.

Fast emeralds:
Enable the "Level select" code two times. Select any stage that features Tails or Knuckles (such as stage 1). Accumulate fifty rings and visit Tails or Knuckles. Press A + Start when the special stage starts for the emerald.

Extra lives:
Accumulate fifty rings, enter the special stage, and get the emerald. Lose your current life, accumulate another set of fifty rings, and re-enter the special stage. Give the rings to the same character used the first time the special stage was entered. The same stage where the emerald was awarded will re-appear. Complete the stage for an extra life. Collect 100 rings for another extra life. Lost your current life and repeat this procedure.

Hint: Tails and Knuckles in Rusty Ruins Act 2:
When you get to the third part, immediate before the X Mark, go off the nearby cliff. Then, go down where the Bumblebee Badnik is located. Destroy that little object with the grass under it. Then, you can get to Tails. On the first part, go to where the Blue Shield is located, next to the first exit. Collect 50 Power Rings, then Spin Dash into that wall that looks pushed back slightly. If you won all the Special Stages so far, with six Emeralds you will get the Last Chaos Emerald.

Hint: Knuckles in Rusty Ruins Act 1:
At the last rotating pair of spiked balls, just before the "X", are two small pillars with a wall that you can Spin Dash through. Once through, return to a thing that sets you spinning, then go to Knuckles to break through the pillars beside him.

Sonic & Knuckles

Bonus rounds:
Insert the Sonic The Hedgehog into the Sonic And Knuckles cartridge. Hold A + B + C and press Start when the "No Way" message is displayed to play the unknown bonus rounds in order. For example, if you keep playing and reach level 12 and want to stop, make a note of the password at the bottom of the screen. Turn off the game and turn it back on, it will restart at level 1 again. Press Down and use the D-Pad to enter the password on the screen. Then, press Start, the level you last played will begin.

Level select:
Begin game play with no other cartridges inserted into the Sonic And Knuckles cartridge. Go to any pulley in the first level and press Left(3), Right(3), Up(3). The sound of a ring being collected will confirm correct code entry. Pause game play and press A to restart the game. Hold A and press Start at the title screen to display a level selection screen.

Alternate level select:
Insert the Sonic The Hedgehog 2 cartridge into the Sonic And Knuckles cartridge. Press Up(3), Down(3), Left, Right, Left, Right at the title screen. A sound will confirm correct code entry. Press A + Start to display the level selection screen. This code will also all rings to be kept if your character is hit.

Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. In Angel Island Zone, grab on to a vine and while swinging on it press Left(3), Right(3), Up(3). A sound will confirm correct code entry. Press Start then A at the title screen to enter the Sound Test.

Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Quickly press Up(2), Down(2), Up(4), after the Sega logo fades and Sonic starts to appear, and before the screen flashes white. The timing of this code is particularly sensitive.

As Sonic, Tails, or Knuckles (Note: This is who you will control when you select a level), go to Angel Island Zone. Find one of the swinging vines (not the vines that go down the other vine, but the ones that go back and forth). Press Left(3), Right(3), Up(3). The sound of a ring will confirm correct code entry. Press Start, then A. Press Up or Down(2) at the title screen to enter the hidden sound test where you can choose any level. (Only the Sonic 3 levels in Sonic 3 but any level in Sonic 3 and Knuckles). To change your character in the sound test, press C. The yellow numbers are your character (00 for Sonic and Tails, 01 for Sonic, 02 for Knuckles, and 03 for Tails.)

Debug mode:
Insert the Sonic The Hedgehog 2 cartridge into the Sonic And Knuckles cartridge. Play songs 1, 9, 9, 4, 1, 0, 1, 8 in order at the level selection screen. Then, select any level, hold A, and press Start. Screen coordinates will appear instead of a score and the number of objects displayed will appear instead of the time remaining. Use one of the following controller actions to enable the corresponding debug code. Note: This code may only be enabled on the first version of the game.

Alternately, insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. First, enable the "Sound Test" option by grabbing hold of a vine in Angel Island. While swinging, press Left(3), Right(3), Up 3). A ring sound will confirm correct code entry. Next, grab any pulley in Mushroom Hill and press Left(3), Right(3), Up(3). The ring sound will confirm correct code entry. Pause game play and press Start. You will be taken to the Sega logo and title screen. Select either the "Sound Test" or "1 player" options. When selecting the level, hold A and press Start.

Alternately, insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Enable the "Debug mode" code and complete the entire Sonic The Hedgehog 3 game. Because it is connected to Sonic and Knuckles, you should go straight from Launch Base to Mushroom Hill and be able to cheat until the end.

Alternately, insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Enable the "Level select" code and go to Mushroom Hill Zone Act I. Hold A the enter time that you are there. Press B to jump. When you reach the first Pull Up machine, press Left(3), Right(3), Up(3). A sound will confirm correct code entry. Return to the level select screen, choose a level, then hold A and press Start.

Object transformation
Press B during game play to change Sonic into a game object. Press A to change into a new object. Press C to place an object on the screen. Press B again to revert back to Sonic. Note: The type of object that may be selectable will vary from level to level.

Invincibility
Sonic is, by default, invincible in debug mode.

Slow motion
Pause game play and hold B.

Restart
Pause game play and press A.

Frame advance
Pause game play and press C.

Sound test:
Press A(2), B, A(2), B(3), A(2), B, C at the title screen to access the sound test for Zone 1. Press A(2), B(2), C(2), Up, Down, Left, Right, A, C, B, A(7) at the title screen to access the sound test for Zone 2. Hold Y and press Up, Left, Start(2) for the last sound test.

Slow motion:
Pause game play during any level or act and rapidly press C. You cannot control the game while in slow motion.

Extra points:
Jump and hit the end of act marker. 100 points are awarded every time the marker is hit.

All Emeralds:
With Sonic The Hedgehog 2, to get all emeralds, enable the "Level select" and "Debug" codes, then play songs 01 06 07 07 07 02 01 06.

Play as Knuckles:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Keep moving right at the character selection screen until Knuckles appears, then press Start. Note: This also changes the ending.

Hyper Sonic, Hyper Knuckles, Super Tails:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. In order to get Hyper Sonic, Hyper Knuckles, and Super Tails, get all the regular emeralds. Once at Mushroom Hill, jump into the flashing ring that Knuckles closes. Then, get all the super emeralds. Get fifty rings and double jump. Sonic will turn into Hyper Sonic, will flash colors, and have stars flashing around him. Knuckles will turn into Hyper Knuckles and blink gray and red. Tails will turn Super, but flashes yellow. His bird friends will also help him; even though the birds might get left behind, Tails is invincible.

Play Death Egg Zones 1 and 2 with Knuckles:
Enable the "Level select" code with Knuckles and go to the level Death Egg Zone 1 or 2. You will be playing Death Egg Zone with Knuckles. Note: You can not defeat the Master in Death Egg Zone 1 as Knuckles.

Fight Robitnik in Mushroom Hill Zone Act 2 as Knuckles:
Get three Chaos Emeralds (no more and do not fail in getting any) in Act 1, and three more in Act 2 (again not failing). Fail at getting the seventh Chaos Emerald before the pulley leading up to the battle with the Act 2 Boss. Find another Chaos Emerald far off to the left and succeed in getting it. Make sure to have well over 50 rings and pass the lamp post slowly (stop just after hitting it). If you see red stars, jump in and get more rings. When out of the goal, power up to Super Knuckles only as you are jumping to get the last three rings. Run over to the "underground" machine and jump on it, standing there after the one jump. You should see Dr. Ivo Robotnik in the machine instead of Robo-Robotnik. It seems to work most of the time.

Secret bonus:
Insert the Sonic The Hedgehog 2 cartridge into the Sonic And Knuckles cartridge. When playing as Knuckles at the second zone, climb up every wall until reaching the top. If you see an extra life there, glide left to find a secret.

Secret stages:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Play "1F" at the sound test screen, then highlight Special Stage one or two and press Start.

Hint: Quick goodies:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. At the start of Angel Island, kill the monkey in the tree and jump on the first gray rock to reveal a bumper spring. Bounce up into the tree, and using the bumper spring hidden in the tree, bounce left to land on the moving platform. The platform will take you to a ring bonus and lightning shield power-up. Using the spring in the tree again, bounce right to land on ground with spikes and a RhinoBot. Jump past these to collect the fire shield. When this is collected, Sonic can use the fire dash attack by pressing C(2).

Hint: Easy big Emeralds:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Enable the "Debug mode" code and have a saved game. Get all of the small emeralds from the Sonic The Hedgehog 3 stages. When you get to Mushroom Hill, find all of the big colored rings after obtaining all of the emeralds in that stage. Then, restart the game.

Hint: Easy lives:
Insert the Sonic The Hedgehog 2 cartridge into the Sonic And Knuckles cartridge. Play as Knuckles and get to the end of Chemical Plant. There will be a wall that you can climb on. Go to the top of it. There will be an extra life there. Glide to the left you will land on another wall and find another extra life. Glide again to the left. You will land on another wall with yet another extra life.

Hint: Mental Sonic:
Enable the "Debug Mode" code. Press B + C during game play. Sonic will go mental, and dash about on the spot, turn upside down, and do other stunts. This can also be done with Tails and Knuckles.

Hint: Anti-gravity Sonic:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge and enable the "Level select" and "Debug mode" codes. Start in any level, and press A while standing still. Sonic will flip upside down and be able to walk on the ceiling. If this is done on a level with no ceiling, like Sky Sanctuary, Sonic will die. This trick can also be done with Tails or Knuckles.

Hint: Knuckles in events:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. On some levels you can see Knuckles in an event. Enable the "Debug mode" code. As Sonic, when an event happens with Knuckles turn into an object and go out of reach of the event. Change back into Sonic and you can play the level with the following effects: Sonic will sometimes get Knuckles' jumping skill; many objects will turn completely or partially red; Knuckles' theme will play; the speed up boxes have pictures of Knuckles' foot; and The 10 ring boxes have pictures of Knuckles' leg. This trick will work in Launch Base Zone Act 1, Launch Base Zone Act 2, Mushroom Hill Zone Act 1, and Mushroom Hill Zone Act 2.

Hint: Blue Knuckles:
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Enable the "Debug mode" and "Level select" codes. Select Sonic and go to The Sky Sanctuary Act 2. Defeat Metal Sonic with Hyper on. Once defeated, you will see a Blue Knuckles in the ending.

Hint: Dr. Robotnik in disguise:
If you play as Knuckles, and have ever wondered who the weird robot-like boss is that takes the place of Dr. Robotnik, it is actually Robotnik in disguise. He is attempting to kill Knuckles so he can take the Master Emerald for himself. Knuckles only finds out that Robotnik is trying to steal the emerald when he is caught trying to take the emerald in the Hidden Palace zone. (If you are playing as Sonic or Tails, this happens after the battle with Knuckles).

Hint: Defeating final Eggman:
After becoming Super Sonic, you will find the big ship. Go in front, so that the ship fires missiles. Make the missiles hit the top right part of ship. After hitting it eight times, it will be destroyed. Eggman will jump into a space suit and fly through space. Pace yourself and get plenty of rings. When you have at least fifteen, go forward quickly and hit the Master Emerald. Do this eight times to complete the game.

Glitch: Alternate Boss weapon (when playing as Knuckles):
Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Usually when playing as Sonic or Tails, the Angel Island Act 1 Boss uses a flame attack occasionally. However, if you play as Knuckles and reach this Boss, it will instead fire rockets and use the flame only when Knuckles is at close range.

Glitch: Change Act 1 Boss Music (Zones 1-6, Sonic 3):
When playing Zones 1 to 6 in Sonic The Hedgehog 3, insert the Sonic The Hedgehog 3 cartridge into the console without using the Sonic And Knuckles cartridge at all. Instead of the Sonic and Knuckles Act 1 Boss music, you hear the Sonic 3 version (a funky rap backbeat with fun-style music). Knuckles' theme music also changes, taking just the beat from the Act 1 Boss songand putting that in instead.

Glitch: Upside down characters:
This trick will turn Sonic, Tails, or Knuckles upside-down. Insert the Sonic The Hedgehog 3 cartridge into the Sonic And Knuckles cartridge. Enable "Debug mode", select any level, then press A. If there is no roof, your character will die. If you want to return to the ground, press A again.

Glitch: Blue Knuckles with two tails:
Enable the "Level select" code. Choose Tails (02) and choose Sky Sancuary Act 2. Defeat Mecha Super Sonic. After the screen turns white, Sonic and Tails' plane should appear. Sonic will be flying the plane and a blue Knuckles with tails exactly like Tails' can be seen. You can see the tails in the same size when the plane goes away.