I really like Julian's method for this. Be sure to checkmark "Include Mature Games" if you want that (broadens search, includes more). Likewise you can pre-filter out Paid Games, if needed. Of course it would be cool if an EXCLUDE could be added to the Advanced Search, and I think there is a long active Suggestion for that, that Coal-Powered is most likely already in. Note that finding the MOST rare and unusual Roll20 games is sometimes under the "Other Games" category, or the "Board Games" or "Card Games" sections also.