@niss @Felthry Doilus Stage is a glitch from Sonic the Hedgehog 3. If you access the bonus stage from the level select, rather than from inside a level, the game doesn't know where to send you back to, so it dumps you right back into the bonus stage. When it does, the title card is corrupted, and for some reason is says Doilus instead of Bonus. As far as I know, no one knows why.

@terrana @niss That's rather amusing, I like it.

As we recall, the level select was a last-minute addition, so it makes sense things weren't fully tested with it. (We've heard that Sega at the time refused to publish anything that could possibly crash, so they essentially wrapped the entire game in a try() structure and had the catch() be the level select, saying "you found the secret level select")

at least i think that was sonic 3 where they did that
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@Felthry @niss The level select was so incredibly rushed that it still used Sonic 2's level icons. It also contained several inaccessible levels from Sonic and Knuckles, because splitting S3 into S&K was also a rather late decision, when they realized they simply weren't going to be ready for their deadline. The Sonic series has always been like this, and still is.

The "secret level select" crash was Sonic 3D. That went in because the developer was having trouble finding and fixing a crash bug to pass certification, so it went in as a quick hack. (Source for this is the dev himself: https://youtu.be/ZZs2HUW9tDA )

@terrana @niss Sonic has always been a bit of a mess when it comes to program quality, hasn't it? We always kinda thought it was just the 3d ones that were a real mess, but it looks more like it's just the 3d ones are a mess in more immediately obvious ways
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@terrana @Felthry ah yes that was it, thanks

@terrana @niss @Felthry It reads doilus instead of bonus because it loads the artwork using the Angel Island Zone load sequence information