I can post pictures of this very rare catalog Dragonriders of the Styx playset thanks to David Pietila. David says it is the Sears version and he should know. This set seems to be missing the dragon, but that does not mean it wasn't included originally. This was David's childhood set. Here is what he has to say about its background:
Greetings,
I have found a box of Dragonriders of Styx that has been in storage at my Mother's for years. Apologies for the pics, but the item is 19 hours away from me. I had someone else send my photos. The box has instructions, I believe there is an order form on the other side. My mom had written on the box "If you boys open this again I will return it to the store." The box is a plain mailer, at one time it had a label that was plain as well.