And that makes 100% completion today.
Scrap Brain isn't as bad as Labyrinth Zone but it's close. Pro tip: Go really fucking slow. I know, it sucks, but that is how you beat it. Every single trap feels like it's asking you to rush past it so you miss signposting and get zapped or murdered, and there are blocks that you have to wait to appear. Enemy design isn't nearly as bad as Labyrinth Zone, though, just traps are worse. That being said, having to play through it so slow to function is distressing, if not the antithesis to what the game seemingly wants?
The final boss? No rings. I thankfully got through it unscathed, finding the electric balls easy to react to, and positioning myself so I always had an out. Never got hit once, although asking for the player to never get hit is still asking too much. Made the boss kind of a joke for me, though. If you're impatient, you're dead.
The last three achievements on RetroAchievements were invented by people who felt like abusing the player, at least in my book. Completing Marble Zone in less than 90 seconds is a neat challenge, and actually not that hard to do. The underachiever and 200 rings achievements? Ridiculous. The underachiever asks you to wait 5 minutes in every stage of Green Hill, and have 0 rings when you get there, AND have hit no enemies. Green Hill is already a slightly unfair stage, but now it's completely jacked up, and waiting is painful without speed on emulation. But the 200 rings might be the worst one simply because most stages are in the 210-230 range if they're even close, which means backtracking through each path of a level. I walked out of a stage with only 198 because some were impossible to get in one go, and said fuck it. Time for cheats. I'm not sorry.
24 of 24 achievements.