Leave the game going and let the animated intro play through once. On the second time the animation plays, you will hear an alternate song.
Alternate sound effect in Hydro City
While hanging onto any of the hook switches in Hydro City Zone, press Left(3), Right(3), Up(3) to have the gear boost pads in Hydro City play a voice clip each time you use them. If you entered the code correctly, you will hear a chime. Note: This code is a reference to Sonic And Knuckles; it is the level select code from that game.
Alternative Boost Sound Effect in Hydro City
While hanging onto any of the hook switches in Hydro City Zone enter the code Left, Left, Left, Right, Right, Right, Up, Up, Up. You will hear a ring noise to confirm the code was entered correctly. The gear boost pads in Hydro City will now play a voice clip each time you use them.
Debug Mode
At the Press Start screen, hold down the B + Y buttons simultaneously for a second. This will load the debug menu. From there, you can play any level, bonus stages, and preview all the games songs via the Sound Test option. To navigate the screen, use the D-pad and press A to make a selection.
Fight the true Final Boss
As Sonic, collect all 7 Chaos Emeralds before finishing Titanic Monarch Act 2. After beating the normal boss of Titanic Monarch Act 2, Sonic will be teleported to the true final boss.
Infinite Lives
When you enter Press Garden Act 1, look for the first ink container you see (that spawns the hopping badniks) stand next to it and do a spindash to kill the badnik. Let go of your spin dash and let another badnik come out. and repeat. The points will start stacking up to give you free lives. (This is akin to Sonic 3's Oil Ocean bird Infinite Lives trick) Note: You cannot hold the spindash down, you must release in between for another badnik to spawn. Alternatively, using Super Sonic you can stand there and do the same.
Mean Bean Mode
Dr. Robotnik's Mean Bean Machine is a Genesis game based on the Puyo Puyo franchise, and it's even referenced in Sonic Mania as a main boss. If you want to unlock a mode to freely play it you'd need to get 21 medals (silver or gold) from the bonus stages where you have to get the blue spheres and avoid the red spheres. The medals do stock for different playthroughs of the game.
More Blue Sphere Bonus Stages
To unlock this in the Extras menu, get all the medals (silver or gold) from the bonus stages where you collect the blue spheres while avoiding the red ones. You'll be able to play extra bonus stages where you have to touch a green spheres to make it turn to blue.
Play as Super Sonic
Collect all seven Chaos Emerald in the special stages to unlock Super Sonic.
