In my SRB2 mod, I decided to, instead of using them for permanent life increases as was previously intended, use rings as currency for shops. Above is an intended sprite for one shopkeeper, a burrowing owl.

Addendum: Upon looking again at images of burrowing owls, I have noticed that I should probably change the coloration or the eyes, changing the white to a light yellow.

Addendum 2: Since the upload of this image on DA and Weasyl, the SRB2 mod project has gone on possibly indefinite haitus.