sonic-mania
While working on my Blue Sphere unlock guide, I've started noticing that the bonus stages sometimes repeat themselves.
This means that, unlike the standalone Blue Sphere (which had 134,217,728 levels), Sonic Mania most likely has a limited pool of pre-made bonus stages.
How many unique Blue Sphere bonus stages are in Sonic Mania?
Completing a Blue Sphere bonus stage earns you silver and gold medals which unlock Extras and Secrets. There are 32 medals to collect in total to unlock every Extra and Secret.
Medals are carried over between playthroughs, meaning you can play though the game multiple times on different save files to get them all.
*Actual number of medals required may be less.
To open the Secrets Menu, highlight the ‘No Save’ section in the file select in Mania Mode. The will now have a new button labeled 'Secrets'. (△ on PS4; X on Switch; Y on Xbox). Note that the Secrets Menu can only be used in 'No Save' mode.
The Extras Menu can be found at the bottom of the Main Menu below "Competition" and "Options". You can track your collected medals here.
According to Eurogamer, collecting every ring in a bonus stage earns you a 'Perfect', which is required for getting a Gold Metal.
The trick to getting a Perfect is to collect every ring on a stage. You may notice you can finish a stage without collecting all the rings, despite seemingly collecting all you can see; that's because you can convert spheres into rings by creating an outline around groups of blue spheres. These can be squares or rectangles, groups that already have partial outlines already completed, or have unusual shapes, such as bouncing spheres cutting into the corners.
The trick, then, is to make sure you have converted all groups of blue spheres into rings before you collect any remaining individual blue spheres. The easiest way to do this is to leave behind one or two blue spheres that cannot be converted, getting the 'Perfect', then going back to those spheres you left.
It's worth noting that, as mentioned in our Sonic Mania unlockables page, getting all gold medals doesn't unlock anything in game - only Silvers is required. It's only if you want all Trophies or Achievements that Gold is worth aiming for.
Screenshot from Giantbomb's 'Quick Look: Sonic Mania'
Best Answer
Sonic Mania has 32 premade Blue Sphere bonus stages accessible from checkpoints.1,2,3
Additionally, collecting 32 medals will unlock a near infinite supply of randomly generated Blue Sphere stages in the Extras Menu.
For reference, GameXplain has a 50 minute video showcasing all 32 premade bonus stages.
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