Enable the "Level select" code. Then, play songs "04", "01", "02", and "06" in order at the "Sound Test" menu.
Change Tails' name to "Miles"
When the SEGA logo fully appears (After Sonic has run accross it in both directions), tap the letters A, G, E, S in that order. If done correctly, the sound of a ring being collected will play. In gameplay, Tails' name will read "Miles".
Cheat mode
Select "No Save" mode then plus for Sonic. Tap the letters "S", "E", "G", and "A" in order at the at the Sega screen. A sound will confirm correct code entry. Hold two fingers on "Start" at the bottom of the screen and slide them to the top of the screen when the title screen appears. If done correctly, the level selection screen should appear, as well as various cheat options.
Debug mode
Enable the "Level select" code. Then, play songs "01", "09", "09", "02", "01", "01", "02", and "04" in order at the "Sound Test" menu. Start a level, then tap the score display at the top-left corner of the screen during game play to toggle Debug mode. Use the "-" and "+" to change objects, then jump to place that object at your current location.
Level select
Start A No-save game and select who ever, Then as S-E-G-A Appears fully tap each letter in order and you will hear a ring chime, Then at the title screen press 2 fingers on the screen and you will be taken to level select.
Proto Hidden Palace to Emerald Hill Zone time warp
Start a game in no-save-mode, tap each letter of S-E-G-A IN THAT ORDER with your entire fingerprint, then when the background of the title screen appears, tap with two of your fingers on the bottom half of the screen, to get to the level select screen, select sound check with 00 selected three times, and select the duo of knuckles and tails, do the Proto Hidden Palace cheat, REMEMBER TO ACTIVATE DEBUG MODE FIRST, afterwards, once loaded into Proto Palace Zone, become and place an S-Monitor, bust it, go super, place and break more, then place five checkpoints REALLY close to each other, activate ALL them, then go to the one in the center, jump in the star ring(s), collect the emerald by successfully completing the special stage, then you should be warped all the way back to the beginning of the game, in Emerald Hill Zone.
Various Achievements
Complete the indicated task to unlock the corresponding achievement.
Achievement
How to unlock
100% Chemical Free (5,000 experience points)
Complete Chemical Plant without going underwater.
A Secret Revealed (10,000 experience points)
Find and complete Hidden Palace Zone.
Beat the Clock (10,000 experience points)
Complete the Time Attack Mode in less than 45 minutes.
Bop Non-stop (10,000 experience points)
Defeat any boss in 8 consecutive hits without touching the ground.
Early Bird Special (10,000 experience points)
Collect all the Chaos Emeralds before Chemical Plant.
Head 2 Head (10,000 experience points)
Win a 2P Versus game against a friend.
Hit it Big (5,000 experience points)
Get a jackpot on the Casino Night slot machines.
Metropolis Master (10,000 experience points)
Complete any Metropolis Zone Act without getting hurt.
Perfectionist (10,000 experience points)
Get a 'Perfect Bonus' by collecting every ring in an Act.
Quick Run (5,000 experience points)
Complete Emerald Hill Zone Act 1 in under 35 seconds.
Scrambled Egg (10,000 experience points)
Defeat Dr. Eggman's Boss Attack mode in under 7 seconds.
All Chaos Emeralds...