Flicky Island

Flicky Island (referred to as Flickies' Island in comic sources) is the setting for Sonic 3D. The island is presumably not too far removed from South Island, as Sonic occasionally stops by on his travels to check up on his friends, the Flickies: brightly-colored birds which have been seen all over since the very first game.

However, the Flickies that reside in Flicky Island are special; they are native to another dimension, and travel to and from between the worlds using giant rings. While such metaphysical chicanery doesn't faze Sonic, the megalomaniac Doctor Ivo Robotnik becomes very interested in the Flickies' powers after learning about the island. Robotnik resolves to roboticize the inter-dimensional creatures, and harness their strange abilities to further his search for the Chaos Emeralds - thereby setting in motion the events of Sonic 3D.

Locations
As with South Island, Flicky Island manages to pack an impressive array of facilities and climates inside its coastline. The only game which has visited Flicky Island is Sonic 3D, and all its levels are sited there:
 * Green Grove Zone, a Green-Hill-esque tropical paradise with checkered soil.
 * Rusty Ruin Zone, the once-submerged remnants of an ancient culture, dredged up from the sea bed by Robotnik.
 * Spring Stadium Zone, a bouncy arena filled with balloons and spikes.
 * Diamond Dust Zone, the frigid slopes of Flicky Island's mountain range.
 * Volcano Valley Zone, an active volcano.
 * Gene Gadget Zone, Robotnik's genetic research laboratory.
 * Panic Puppet Zone, a fortified factory and the center of Robotnik's base (presumably destroyed).
 * The Final Fight, the steel foundations beneath Panic Puppet (presumably destroyed).

Sonic the Comic
In the Fleetway Sonic the Comic series, Robotnik was ousted from power as the dictator of Mobius in issue #100. He claimed that he had always planned to someday investigate the mysteries of Flickies' Island, in particular why the Flickies themselves were only ever seen for a few weeks every year and where they went to. Robotnik discovered that the Flickies' were in fact from another dimension, and traveled to Mobius through a floating Mobius Ring in an ancient ruin on the Island. Robotnik set about catching the Flickies to serve as organic batteries for his new Badniks, with which he intended to regain control of the planet.

However, his plan was thwarted by the intervention of the Drakon Empire, who had built the ruins on Flickies' Island long ago and left the Mobius Rings as a way of knowing when the Mobians had developed to the point where they could be a potential threat to them. Robotnik was captured by a Drakon Prosecutor and taken through the Mobius Ring to the Drakon homeworld, and the Mobius Ring was deactivated.

After making a deal with the inter-dimensional Drakon, Robotnik ran his operations from Flickies' Island and attacked Mobius repeatedly with his new model Badniks.

After Robotnik's apparent demise, Sonic led the Freedom Fighters on a mission to Flickies' Island to destroy Robotnik's base. However, they were ambushed and captured by Agent X. Although Sonic was briefly teleported to the Shadow Dimension, the Freedom Fighters managed to escape and apprehend Agent X, then rescue Sonic. In the commotion, Agent X damaged a matter transporter, causing it to overload. Sonic and his friends escaped before the resulting explosion destroyed Robotnik's base.

Although the island was now deserted again, Robotnik's automatic defenses were still functional, including gun turrets, pit traps, and a robot gorilla. When a group of holidaymakers arrived on the island (as part of one of Max Gamble's money-making schemes), these defenses became active and endangered the tourists. Fortunately, the tourists were rescued by Sonic and Tails, and Sonic used his super speed to disable all of the island's automated defenses.

Archie Comics
In the Archie's Sonic the Hedgehog comics, Flickies' Island is featured one time as main setting in Sonic Blast special. In the story, Sonic responds to a distress call from Flickies' Island, arriving to find that Doctor Robotnik had captured the island, roboticized the Flickies, and was in the midst of a search for the Chaos Emeralds. Sonic soon found out that the robot Flickies were vulnerable to seawater, and reverted to their flesh and blood forms on contact. Sonic raced through the Zones and defeated Robotnik in the Techno Bodyshell Battlesuit, causing Robotnik to flee.