After opening the game’s main executable (Start.dol) in BrawlBox’s memory editor, I was able to find references to a SceneInit.cpp (C++) file.
Based on the name, I assume that SceneInit would be called whenever loading (i.e. initializing) the game (scenery). This function would then need to load certain files (models, textures, etc) from a mainchapter file (e.g. mainchapter2.arc.clz).
In addition, there are also references to common.arc.clz and preload.arc.clz, possibly related to a FileUpdater.cpp function.
I’m going to post some of my findings on ZenHax. Hopefully someone there will be able to provide some additional insight.