"Virtual Danger" is the fortieth episode of the Sonic Underground television series and the final episode overall. It first aired on 23 May 1999 in France and on 22 October 1999 in the United States. It was included in Volume 2 and Band on the Run.
The song performed in this episode is "Don't Let Your Guard Down."
Sonic and Manic are introduced playing "Castle Conquest", a game of virtual reality, in order to enhance their pilot skills. When the two brothers decide to put their practice to use, they fly in a successful mission that intercepts a supply ship from Robotnik. Afterwards, they continue to play the game, only to run into a rival, Destructo. Destructo states that he is a programmer for the game and offers to give Sonic and Manic two updates. After downloading the second one, however, Destructo reveals that he is, in fact, Robotnik in disguise. He then reveals that he plans on using the updates to trap the two hedgehogs in the virtual universe and permanently kill them. Once the virtual danger of the game becomes a reality, it is up to Sonia to play the game to save her brothers.
- The triplets were supposed to reunite with their mother, which would fulfill the prophecy, defeat Robotnik, and restore everything, but the outcome was never resolved when the series was cancelled.