Learning about the regional differences between video games is always one of the odder things involved in looking into the subject. Games getting harder because something important got dummied out, overseas releases being more polished because they had more time to finish the product, cultural references being removed because they're "too foreign," and occasionally the "American Kirby is Hardcore" effect (characters being at least partly redesigned to look "cooler").
The game Ristar, which I recently became aware of because of the tiny Sega Genesis collection console my sister picked up, has a fistful of these things...
...which is all the stranger because apparently the two versions were actually released about a day apart.
I don't have much else to say about Ristar beyond the fact that I rather like the game overall; out of the games on the console, I've probably played it more than any of the others because its playstyle, at least on the first world, is fairly easygoing and doesn't punish patience, which is suited to me. (The other competitor for my most-played game is Mean Bean Machine, which I probably shouldn't play as much as I do because I'm bad at it, the computer cheats, and I'm enough better than everyone I might play two-player with despite being bad at it that it wouldn't be fair, and also I don't think Mean Bean Machine is a game that should be played between friends.) Never gotten past the first little tiny stretch of the third world, though-my kid brother got to the fourth world today, though, so good for him.**
Anyway, have the final boss theme. Ristar generally has good music, and Kaiser Greedy's theme is particularly so.
I actually kind of like Kaiser Greedy himself, for that matter; he's got kind of a "Castlevania Dracula" vibe, but is also a cartoony space demon.
*He crashes into walls, smashes his foes, bops around like some sort of deranged pinball occasionally, and flies face-first like a comet through space. He's pretty hardcore for a guy with four hitpoints.
**He was using a strategy that I came up with, though I don't think he remembered me suggesting it, that involved farming lives on the first bit of the first stage. There's a hidden extra life you can get a very short distance from the starting area, and an obvious extra life that you can find a little ways further in. Grab both and lose a life on purpose and the extra lives respawn, letting you get one more extra life for each loop than you're losing. Kid bro gathered about two dozen before plunging into the best run he's had on the game, getting to the main boss of the fourth world before he had to head home for the night.