The Doomsday Project (Sonic the Hedgehog)

"The Doomsday Project" is the thirteenth and final episode of the American-Italian animated series Sonic the Hedgehog, and the twenty-sixth episode overall. In the episode, Robotnik begins his doomsday project a week early, leading to the Freedom Fighter to start their final attack.

The episode was originally aired on December 3, 1994 and was initially meant to be continued with a third season sometime in September 1995. But due to production issues (including ABC continually moving around the show's schedule), the show was cancelled leaving the series on a indefinite cliffhanger.

Plot Synopsis
However the scene cuts to the remnants of Robotropolis revealing Snively survived the explosion and the episode ends with Snively taking Robotnik's place, before menacing red eyes appear.