What's was that game called again?

A long time ago maybe when I was 4-6 years old I walked into a store. I found either a ps2 (probably) or a psx(maybe) with a game demo playing. I tried it out and loved it since then I've become a gaming pro, not an addict(tested) but a pro. yet I can't seem to find that one game anywhere. I don't remember the name but I remember the details. You're some kind of hero who can change into a beast and a plant that shoots seeds but can't move. It might have something to do with rings. I really want to find that game but I haven't been able to find it so far. If anyone could tell me what this game is called I would greatly appreciate it.