"Friend or Foe?" is the sixteenth episode of the Sonic Underground television series. It first aired on 28 February 1999 in France and on 20 September 1999 in the United States. It was included in Volume 1 and Secrets of the Chaos Emerald.
The song performed in this episode is "Not Always What They Seem".
The Hedgehogs converge on the Floating Island, in their latest attempt to find their Mother. Sleet and Dingo also have an interest in this island that involves the Chaos Emerald, which is the island's life-force. But, before either party can achieve their goals, they have to get through Knuckles, the floating islands stern guardian. Knuckles is even skeptical of Sonic's motives, although he can see right through Sleet and Dingo. Once the Hedgehogs convince Knuckles they are friendly and mean no harm to his island, they help Knuckles in protecting his exotic home and the emerald.