i mean, they did use tiles for the rotating platform in iggy's fight. anyways, for sprite limitations, up to 32 16x16 sprites can be displayed at a time, with the colors being limited to the current palette (shared by the background tiles), and only one color per row. in this game, most sprites overlap to give up to three colors per row. as for background tiles, they're all 8x8, and can only have 2 colors per row. things like the question blocks are 4 tiles overlapped with a sprite, and things like goombas and mushrooms are made of 2 sprites, while things like mario and yoshi consist of 4 sprites each. in this case though, bowser uses 12 sprites

I think, considering the fact that The Big Boo and those bubble things are shrunken down considerably in this, that the true reason the OG Bowser fight isn't in this is due to sprite size limitations. I'm not sure of the MSX2's limitations, but it is also entirely possible they were not able to use BG tiles for Bowser like what the OG game does as well.

@chirpet but the Mode 7 isn't really used in any of the attacks, and only used for the transition between the fire segment and the other segments, and when hurt. It would've been easy to just make those animations not use it

If I had to guess, I would say it's because of the use of mode 7 in the SNES version's bowser fight.

interesting how they gave bowser an original fight