Sonic 3D Blast

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.

Alternate ending:
Usually the game ends with the final Boss escaping after his defeat in the seventh zone of Act 3. If you acquire all seven Chaos Emeralds you will be teleported to the final Boss fight area.
Information in this section was contributed by cassensjim.

Hint: Rusty Ruins Act 2: Tails and Knuckles:
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.
Information in this section was contributed by SonicD3.

Hint: Rusty Ruins Act 1: Knuckles:
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.
Information in this section was contributed by Vaslovic.

Hint: Volcano Valley Act 3: Quick victory:
The moment the level starts, grab some rings then jump onto the pipes. Stand between the steam vents and where Robotnik lands. Just before Robotnik lands, jump to hit him. You must time correctly so that you hit him a mere moment after he lands. Then, continuously jump and hit him. You will need to land in the location between the steam vents and Robotnik or you will get hit and lose rings and time. By using a combination of the D-pad and how long you hold [Jump], you will be able to keep attacking even when the fire snake comes out without getting hit. If done correctly, you can defeat the Boss and complete the stage in 20 seconds.
Information in this section was contributed by Bluehog.

Hint: Secret passage to Special Stage:
Go to the second speed up tile that you find on the level. You should be in front of a wall with a small crack in it. Super Dash on that crack. You will find that you are going through a secret passage. Go into the cannon and press A. You should be near Knuckles. Go up to him, and if you have at least 50 rings, you can teleport to the special stage.
Information in this section was contributed by Michael Obed.

Hint: Staying safe on spikes:
To stay safe on the spikes, such as the Spring Stadium, keep jumping. Every time you jump the spikes will retract, leaving safe ground to land then. As soon as you do, jump again and repeat the process.
Information in this section was contributed by Travis Schwipps.