Ok, PornPorn69, not to hate on your Ideas which some I like, but remember, Bowser's Castle was a playshape game, and to finish it, you have to think what would playshape added in or changed.
things I liked about your ideas, adding Rarewere characters, which like you also notice or should have noticed from the original version where you didn't, Berri and conker where in the game. No need to go much deeper with Rarewere than that.
second thing I liked, more interactions, but that one is just or should be a know thing that is going to happen with the people picking up the project.
With you character variation, liked it up to the point of adding the T.V. female side kicks of pokemon, doesn't seem like something playshapes would do. But, if you want that, why not play the Pokémon Unscensored game on this site?
Last thing I liked was your Idea of adding music, which I also see being add in no matter what at some point.
Ideas that I'm iffy about is was SSB characters, to many characters will take years to finish this project that will take maybe two years at the least to finish as is with all the characters playshape original decided to add in.
Things I will have to disagree on
Adding to many Rarewere or Capcom characters, like your Megaman. This is more of a Nintendo based game, but who knows, maybe someone on this site will read your comment and start a Megaman game.
adding in power ups, would go off the main point of the game, for this is not a start to finish multiple level game.
Multiple worlds, I personally hate this idea for then we would just be making a never ending updating game like another playshape project, Mario is Missing. Not a single version of playshapes original version of this game showed multiple levels and would just feel weird knowing this was meant to be a one Huge level game.
Different Playable Characters, this is more of a Mario game and a simple pallet swap on Mario is easy to handle for the entirety of the game's events, a different character sprite would not only add on to the huge length of programming time but also once again, stray of from playshapes original intentions.
and just no, with how you think the final boss should be, just no, doesn't even sound right in any way.