First of all, hi, I'm new and I found this site while doing a search for info on the prototypes I referred in the topic's title, namely Sega's Batman Returns.
In a recent retro-gaming "trip" I saw some old, back from 1992, previews of these two games in old magazines. I saw some unseen pics in GamePro and Sega Visions (both the US versions).
In Sega Visions # 10 pg. 23 there's a screenshot from the Mega Drive version showing the exterior of a Castlevania-like cathedral with flying buttresses, with a colour scheme of the level similar to the interior of the cathedral included in the finished product (in Act I for those familiar with the game).
Also, in the CD racing section in a pic I saw in GamePro clearly shows the Batmobile ready to pass through a tunnel located under one of those huge statues present in the platform section.
I'd be very interested in having access to some more info/pics or even the prototypes themselves :) I know they may not the best or more interesting games for most people, but back in the day some played them a lot :)