Li'l Judd did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
“Okay, I’ll be the first to admit he’s adorable, but from what we’ve been able to observe, he’s gunning for Judd’s spot as premier Turf War judge like a bloodthirsty tiger crouching in the jungle underbrush. The details of his origins are still shrouded in mystery, but rest assured our research on this fuzzy subject will continue.”
— Splatoon Official tumblr
Li'l Judd is a tiny kitten from the Splatoon series, and one of the few land mammals shown in the franchise. He's essentially a tiny version of Judd and accompanies the older cat as a Turf War referee, usually on the side of the opposing team.
Despite his adorable appearance, Li'l Judd has a burning desire to take over Judd's role as premier Turf War referee. Like Judd, his origins are somewhat unknown.
Li'l Judd can be described at a tinier, fuzzier version of Judd, being a kitten and all. As such, Li'l Judd is also plump, has an arrow-shaped tail, and his patterns also resembles a tuxedo and a bow tie, albeit in a lighter shade of gray. The biggest difference is that Li'l Judd has small, black beady eyes, instead of the yellow eyes Judd has.