The fish mask beltboy probably is a leftover from Yoshi's part of the game. He never mentioned any plans for it.
As for any bugs you will have to tell me all of them if you would like me to fix them but your engagement is generally very appreciated.
I've replayed the game and recorded the bugs
https://mega.nz/folder/Bu4VSTZL#iU4ASVPkGek6D4iBZjQWXw