Warp Ring

Warp Rings are large highly-advanced technological golden rings that when powered by Chaos Energy allows for traveling between anywhere in Sonic the Hedgehog's world and different Zones.

History
In Archie Comics' Sonic the Hedgehog comic book series, the Warp Rings were invented by Dr. Finitevus following his mutation when he drained power from Chaos Knuckles. When Drs. Eggman and Wily altered reality with a Genesis Wave, Warp Rings were employed by them, despite Eggman's previous lack of access to the technology in his original reality.

After stealing a Chaos Emerald from the Mega City bank, Tails Man opens up a Warp Ring for him and the other Roboticized Masters to escape. Mega Man follows through it, leading to the Green Hill Zone. (Sonic Universe #51)

Dr. Light manages to recreate the Warp Ring's energy, causing it to reopen the portal to the Zone. Mega Man manages to trick Sonic the Hedgehog (whom he's fighting) in to coming with him through the Warp Ring, with both ending up in Mega City. (Sonic the Hedgehog #248)

The two continue their fight, only to call a truce when Tails Man is sent after them. After the battle, Bass and Metal Sonic arrive at Light Labs to capture Dr. Light. Mega Man, Sonic and Tails (restored to his original form) arrives too late to stop them. Tails manages to recreate the process needed to open a ring and he, Sonic, Mega Man, Rush and Proto Man enter to find themselves in the Skull Egg Zone. (Mega Man #24)

Later on, Roll manages to open another Warp Ring, allowing Duo to join the others, and later Dr. Light's original eight Robot Masters. (Mega Man #27, Sonic the Hedgehog #251)