It has been a long long time since I tried modding the wii but I kept what I used and such on my pc.
You will need brawlbox. If I remember correctly sound fx are in phantom_snd.brsar but also I remember getting some voice lineshttps://github.com/libertyernie/brawltools/releases
Also the folder phantomsound should be under but on the wii file systeme or disc image I think the game should be called R96PAF for PAL and might be something else for ntsc.
I could have sworn there was another tool I used but I don't remember it yet.
In my really old mod I changed The windmill song to the Noxious Lalakoosha theme from Klonoa 2 but for some reason I couldn't get the sound to loop like it was supposed too.
Edit: oh yeah also these files affect enemy placement and what object spawn in what part of a vision however I don't know how to edit them directly. Swapping them around has various interesting results like getting rangolango to appear at the start of vision 1-1 but most of the time things just crash