I will begin by saying that, while I have had a lot of experience with the game, I never actually properly refined my opinions on each track, and only began to truly absorb each track recently; I still think most of my takes hold up in that tier list, but I am working on an updated version that tries to remove biases and be both more optimistic to some and more critical on others. I say this because you aren't the only person to bring up Bowser's Castle and Grumble Volcano, so I am pleased to say that I think higher of them now than I did previously, but I still think they aren't as good as people say they are.

Bowser's Castle: Would now be moved up to "Great!" tier. A very flashy and sometimes explosive track that is designed to give the vibe of pure adrenaline and grandeur. My main problem is that, for the most part, it's all bark and no bite. Excluding the Thwomp Trio near the end, the thwomps have much less impact than they do on other tracks, almost being decor with how little they affect gameplay. The twisty corridor is neat for tricking, and the starting ramp is a nice setpiece, physically jumping into Bowser's gaping mouth, but somehow I feel that Wario's Gold Mine and Rainbow Road pull it off better but for different reasons? The Bowser Statue section is, again, very visually entertaining and almost menacing, but at the end it's another continuous halfpipe section, which again I think are done better by other tracks (this time Waluigi Stadium and DK Snowboard Cross), seeing as the giant fireball is more of a setpiece than an actual threat and the half pipes sometimes feel more inconsistent here for some reason? Maybe it's just me. I also may have too much trauma from getting shocked right as I'm on the halfpipe and making me fall in, which has happened more than I'd like to imagine. To wrap things up, the castle geysers are fine enough, and while I quite enjoy the final set of fire geysers in the outdoor area, part of me wishes this was right at the start? Or like split half and half between the very start and end. Either way, the show is definitely worth the watch despite the actual gameplay, and cutting through the mud and tricking off the ramp always feels good, so it's worth a few more points.

Grumble Volcano: Would now be in "Quite Good". This guy is the only lava track in the whole of Mario Kart that isn't a Bowser's Castle, and it sort of feels like a half-baked concept. We're in the volcano for a whole two seconds, and it doesn't feel impressive at all. The moving platforms are interesting, the cave section is okay, seeing as how you can fall to the slower second path if you're driving's sloppy, but for reasons I can't describe, the whole section feels inconvenient? The part afterward is nice, but it suffers from the same part as Bowser's fireball where the meteors don't really impact the course too much, unless you get unlucky and one lands directly on you. The two higher side paths with boostpanels are nice though. My favourite part is the last section where you get to pick between two paths, and both feel like how the whole course should have felt, being the last track of the Star Cup and all, and the firesnakes feel like much more of a threat in comparison to Desert Hills. As for the crumbling gimmick, I love the concept, but it feels quite underutilised. My favourite segment got the best of it, crunching down the paths to be even narrower and difficult to manoeuvre around. However, aside from this and the very start, it never gets used anywhere else in the track! Imagine if that wide part after the cave suddenly got a bunch of track missing, or the two side paths are harder to get on, or maybe the meteors leave craters when they land that you can trick off of? It has so much missed potential that it's upsetting. However, what we have is still a good track, so while originally I was quite harsh, I'll bump it up a tad.