From Sonic Retro
Eggrobo (エッグロボ), or occasionally Eggmanrobo in Japan, are android badniks who make their first appearance in Sonic & Knuckles' Sky Sanctuary Zone. Shaped like an egg with arms and legs (clearly made to resemble Dr. Eggman), Eggrobos hover in place and attack with a laser pistol.
Sonic 3 & Knuckles
In Sonic or Tails' stories through Sonic 3 & Knuckles, Eggrobos are first seen during the cutscene at the start of Sky Sanctuary Zone, launching from the Death Egg's equatorial circumference as the great battle station climbs back into space under the power of the Master Emerald. These rotund badniks are the only foes (bar Mecha Sonic) to be found in Sky Sanctuary. The Eggrobo in Sky Sanctuary are seemingly much less resilient to attack than the one Knuckles spends his duration of the story fighting, due to them only needing one attack to destroy.
For Knuckles, however, one of these badniks plays a more integral story role. While Sonic and Tails deal with Eggman himself throughout S3&K, the echidna's boss fights feature an Eggrobo piloting the boss machines during every level except for Flying Battery Zone (and, occasionally, Mushroom Hill Zone). It is unknown canonically why this EggRobo is piloting Dr. Eggman's vehicles unless it either thinks it is Eggman or Dr. Eggman simply gave it commands to do so. Most likely, it was commanded to get the Master Emerald back. This Eggrobo may be the Eggrobo that emerges from the pile of destroyed Eggrobos in Sonic and Tails' Chaos Emerald only endings as Knuckles' storyline takes place after the events of Sonic and Tails'.
Eggrobo is also an unlockable character in Sonic R, with stats and abilities similar to those of Eggman. Sonic Channel featured Japanese language profiles of the Sonic R characters; translated, Eggrobo's is as follows:
Sonic Adventure 2
In the original Dreamcast version of the game, Eggrobo could be downloaded in Eggrobo Kart Racing as a playable character for use in the racing minigame. In the Gamecube remake, he had to be unlocked for use in the racing minigame, by clearing all Rouge the Bat's missions. He was not part of the game's actual story or any normal stage.
Sonic Generations (HD)
In Sonic Generations (HD), the hedgehog revisits Sky Sanctuary Zone to be confronted by the classic Eggrobo opponents. Some of the robots use their rifles rather more dangerously, now, firing not one beam of light but several at once.
In addition, and lacking any official name, variant Missile Eggrobos are enemies found only in this level. Whereas in the original level, the only enemies to appear at all were the classic red/yellow Eggrobos, Act 2 of the Generations stage mixes things up by adding these new. indigo/red versions.
Missile Eggrobos don't carry the Eggrobos' standard laser rifle, instead firing homing missiles out of the top of their heads, which pursue Sonic with some tenacity.
When Eggrobos appeared in the Archie Sonic the Hedgehog comic books, they were referred to as "Eggbots."