Ring Shooter

Ring Shooters are machines and gimmicks, which are seen in Death Egg Zone of Sonic & Knuckles and are later modified to appear at Sky Fortress Zone in Sonic the Hedgehog 4: Episode II. These devices may or may not be created by Doctor Eggman, since they are seen in his air fortresses.

The appearance of the device has varied between these two games, but the most common known feature of this device is sending Sonic and Tails to travel short distances by flying to a different area through yellow rings. After a while yellow rings then guide the characters to the other side.

Sonic & Knuckles
In Death Egg Zone of Sonic & Knuckles, the Ring Shooter is illustrated as a Spin Dash launch pad next to a cyan-colored gate with a 3 second timer and high-voltage fuses on side of the gate. After the countdown has gone to zero, the player is launched through a line of yellow rings as Sonic or Tails are on the Spin Attack mode while flying around the yellow electricity rings. The arenas are large, where the player flies, while doing loops around and other swerves until the player will guided to the other side of the arena. The event is automatic as the player is unable to control the character.

Sonic the Hedgehog 4: Episode II
Ring Shooters are seen years later only at Sky Fortress Zone Act 3 in Sonic the Hedgehog 4, where they are redesigned as yellow, bizarre-looking cannons with a plastic cover over the top. When Sonic and Tails use the Homing Attack on the Ring Shooter, they jumped in and got launched through yellow rings before depositing them in a cylinder that rotates and dumps them on another Ring Shooter at different section of the zone.

Trivia

 * While the machine hasn't been named in Sonic & Knuckles, it has been mentioned in Sega Blog while revealing concept art of the machine for Sonic the Hedgehog 4 in the website.