This is about the anime characters. For the monster itself, see Jill.
The Jills are snowmen-like monsters who live in a cozy village in Brillia. Although their time on the show is brief, the Jills in that village play one of the most pivotal roles in the entire anime series. The animation style makes them seem very seal-like as well.
Several Jills can be seen in the audiences at the various tournament battles in Season 3.