Onyx Island is the main setting of the game Sonic Rivals (December 2007). During the game, it mysteriously appears in the ocean, and various characters travel to the island to investigate. On the island, Tails is turned into a card by Eggman Nega (who is disguised as Doctor Eggman), who uses a special camera.
It is eventually revealed that Onyx Island is a future version of Angel Island, that was warped back in time by Eggman Nega with the power of the Master Emerald. Nega has travelled into the past in order to change his destiny by turning the whole planet into a card that he can control.
Even in the future, Nega mentions that Onyx Island is still the home of the Master Emerald, as he needed to travel to the island to photograph the gem and turn it into a card.
Following Nega's eventual defeat, Knuckles decides to return Onyx Island to the future by using the Master Emerald.
Zones
Five out of Sonic Rivals's six zones are located on Onyx Island, as follows:
The game's final zone, Meteor Base, takes place in space and not on Onyx Island.
Archie Comics
It appears in StH #215, as an island that is standing at sea in a slanted angle. It has a ruined city with a libary that Silver researches. It holds many artworks, including a picture of the Future Freedom Fighters, and a huge statue that looks like Lara-Su. It has been mentioned in one of writer Ian Flynn's question-and-answer sessions, in which Silver mentions that in his time he knows the guardian of Onyx Island.[1]