dolphin is an easy way to inject custom textures into the gamecube/wii era games, so it should theoretically be possible to make custom textures that replace characters with fat versions of themselves. ex: peach
I have absolutely no idea how to go about this or if it is even possible, however.
I looked into how it would be done in TTYD and it’s really simple. here is my proof of doing it
what I did was download the png version of the HD textures and just edited it in gimp. not sure how it would be done on N64 but I know that it can be done there too. it’s probably harder though
Speaking of the original Paper Mario, it might be worth looking into the Star Rod editor. I don’t think it ever allowed users to actually create textures for NPCs, though.
I have seen it be used to make custom enemies and partners. most projects doesn’t have custom NPC’s but I found this video that have one so it is possible