This is not a sequel or spin-off of any of the other earlier "Sonic" programs, but a new series altogether.
Knuckles the Echinda only appears in four episodes. These include Friend or Foe (1999), Flying Fortress: Chaos Emerald Crisis Part 1 (1999), No Hedgehog Is an Island: Chaos Emerald Crisis Part 2 (1999) and New Echidna in Town: Chaos Emerald Crisis Part 3 (1999).
The final Sonic the Hedgehog cartoon to have Jaleel White as the voice of Sonic. White also plays Sonic's siblings Sonia and Manic, as the characters are related, Triplets of Hedgehogs.
This show marks the first appearance of Knuckles in a mainstream television show. It is also the first show in which Tails, another major character, does not appear.
Sonic's mohawk was redesigned to have three rows, along with his teeth being shown more and his eyelids are more visible.