I didn't really use reference, but I did tap into the Feeling I got from thinking about old game art from the gamecube and gba era. I got my start drawing by copying those lil game guides that came with boxes. So nostalgic!
In more technical and less old-man-sentimentality terms, I would study what concept art you can find from that era: this art below matches the style most closely but I pulled a lot from A Wonderful Life (not the remake) as well.
then throw in some of the down to earth chunkiness and watercolors from the gameboy color era sugimori art. I guess that's not really that technical, but that's just how my brain formulates style.
also: use a pink outline, soft yet saturated colors, white highlights, and a watercolor tool :) a basic understanding of clothing folds can also really help in both this style and pretty much anything you draw, though that goes for most of the art "basics," which you can never practice too much of. (I am overdue for practice myself lol) hope that helps! :D