Eggrobo

EggRobo (エッグロボ), also spelled Egg Robo or Eggrobo, is an egg-shaped humanoid robot resembling Dr. Robotnik. It first appeared as an enemy in the game Sonic & Knuckles, but has since then appeared in several other main games and spin-offs.

Sonic & Knuckles
In Sonic's storyline in that game, it only appeared as a standard badnik enemy in the Sky Sanctuary Zone, after being seen launched from the Death Egg.

It is rather more prominent in Knuckles' storyline, as the EggRobo replaces Dr. Robotnik as the end-of-zone boss in every level up until the Hidden Palace Zone (except for Flying Battery Zone). In all of Knuckles' appearances prior to this, he had been allied with Robotnik. It's also implied that the EggRobo in Knuckles' story is the same one that appears in Sonic's imperfect ending (if the Super Emeralds aren't collected), implying that the EggRobo in question survived the Death Egg's destruction.

The EggRobo also appears in cut-scenes in the game. At the beginning of the game, while Knuckles is relaxing along with some of his animal friends in the Mushroom Hill Zone, the EggRobo drops a bomb in their midst that scares his friends away. The EggRobo is destroyed by Mecha Sonic in the Sky Sanctuary Zone (the final level in Knuckles' storyline). The EggRobo restrains Knuckles, allowing Mecha Sonic to charge at him, but Knuckles breaks free and Mecha Sonic destroys the EggRobo instead.

Sonic R
EggRobo later appears in Sonic R as an unlockable character. It has abilities similar to Dr. Robotnik's in that game, being capable of launching missiles, though EggRobo is a bit slow. It is unlocked by getting all the five Sonic Tokens in the Regal Ruin course.

Like Metal Sonic, Tails Doll, and Metal Knuckles, the EggRobo is the robotic counterpart for Doctor Robotnik. He performs almost the same although he cannot travel across water for more than 3 seconds before falling in which is odd because of his rocket boosters.

Sonic Adventure 2
EggRobo also appears in Sonic Adventure 2 as a kart racing VMU Download with his own stage, and again in Sonic Adventure 2: Battle as Rouge the Bat's unlockable sub kart, obtained by getting all the emblems of Rouge's missions.

Sonic Chronicles: The Dark Brotherhood
An EggRobo appears in Sonic Chronicles: The Dark Brotherhood as a cameo next to a Sega Genesis and a Capsule in Metropolis. There is also a boss named 'Egg Bot' fought in Metropolis Ground Zero. However, this one is modeled after Eggman's appearance in later games.

Sonic Generations
EggRobo returns in Sonic Generations as an enemy in Sky Sanctuary, like its original appearance in Sonic & Knuckles. The game also features a different variation of EggRobo in the Modern act which trigger missiles from above the head to player.

Sonic the Comic
An army of EggRobos appeared in the Sonic & Knuckles adaptation from Fleetway Editions' Sonic the Comic. In this series, the EggRobos could be controlled directly by Robotnik from his control room aboard the Death Egg. Each model had cameras fitted into its eyes, allowing Robotnik to see everything, and a voice synthesizer allowed the doctor to communicate directly via the robots. EggRobos could also function as regular badniks without Robotnik's direct control.

Archie Comics
EggRobos also appeared in the Archie Comics continuity. They were built by Snively Robotnik to be part of his own private army, with which he intended to move against his uncle, Doctor Robotnik, and take over Mobius himself. Although Snively referred to them as "EggRobos" in their first appearance, Antoine D'Coolette called them "Eggbots," which was the name used in subsequent appearances.

An army of EggRobos appear in the Skull Egg Zone.

Sonic X (comic)
EggRobo made a cameo on the cover of Sonic X #11.

Trivia

 * The EggRobo does not appear as the boss of the Flying Battery Zone in Knuckles' story. Since the sprites used to model Dr. Robotnik for that boss were different, no equivalent sprites for the EggRobo were ever produced. EggRobo does appear managing the Flying Battery's laser, however.
 * Similarly, there is a glitch to get Robotnik to appear as Knuckles' boss in Mushroom Hill rather than EggRobo. In the Sonic Jam version, this was only partially-fixed; Robotnik does not appear as the boss, but the graphics can show up as corrupted instead.
 * Bosses and sub-bosses in Knuckles' story (piloted by EggRobo) are harder than those in Sonic's story (piloted by Robotnik). An example of this is the boss of Angel Island Zone, which shoots four fireballs at a time rather than two.
 * Sonic Advance games has final boss robots that use title "EggRobo". As such Sonic Advance features a robot named the Super EggRobo, that appears as a boss in the Moon Zone, Sonic Advance 2 has the Super EggRobo Z as a final boss in XX and robot named the Hyper EggRobo appears as a final boss at Altar Emerald in Sonic Advance 3. Despite the name, only first two robots bear any slight resemblance to the particular badnik.
 * In Sonic Generations, the EggRobo is the only enemy robot which shoots its own unique laser weapon. All other robot enemies with projectiles shoot a small yellow energy ball.
 * The Egg Pawn introduced in Sonic Heroes are very simaler to the Egg Robos.