OK, the Tanuki/tanooki leaf is DEFINITELY from Japanese mythology, the mushroom thing, if you ask me, is probably at least partially inspired from mythology, and I don't see the connection with the Piranha plants. I really doubt there are any direct drug references in "Mario" games.
PS-The website's not working right. I keep hitting "reply to topic" and it gives me "error," so you might get multiple copies of this message.