Has some things in common with the Season 1 episode, "Den of the Sleeping Demon". Both are the last episodes of their respective seasons and both introduced a trio of heroes who could have been potential new allies to Thundarr. Also, both hint at potential reunions or spin off series, but these never came to fruition in either case.
Last episode of the series.
The location of this episode is a little more confusing that other episodes in the series. Valerie's location in the past and the water tower in the canyon where Cinda lived all implies that this story takes place in North America. However, the ruined city of Endor bears resemblance to Ancient Egypt. It could be that Endor is actually Mayan and this story takes place on North or South American soil.