This is a little bit of a sad thing because I just started homebrewing for the very first time.
What IS a .rel, and do you need to use them for custom characters/textures loaded to Brawlvault?
Because that's pretty much all I want to do so far.
Why is it sad, everybody starts where you are now at some point.
A .rel is a file used to port a character or stage over another. Such as the Scott Pilgrim psa (originally over Lucas) ported to both Jigglypuff, and Mr Game & Watch. You would need a ft_purin.rel for porting Scott to Jigglypuff, or a ft_gamewatch.rel for porting Scott to Game & Watch. In order to actually have Scott over either of these characters you need his psa .pac, and texture .pacs in the character you want him over folder (e.g. over Game & Watch, the pacs would go in the gamewatch folder.
Or as with stages, you'd use (for example) an st_final.rel for porting a stage over Final Destination.
The .rels go in the "private<Wii<App<RSBE(P)(J)<pf<Module" folder
RSBE - NSTC (US)
RSBP - PAL (Europe)
RSBJ - NTSC-J (Japan)