In Sonic's storyline, the Eggrobos appear in Sky Sanctuary Zone. After a brief opening scene showing the Eggrobos launching from the Death Egg, they could be encountered throughout the level as regular enemies.
When Sonic beats the game with all the Chaos Emeralds, an extra scene plays with a single Eggrobo rising from a pile of scrapped Eggrobos. This is believed to be the same Eggrobo that appears when playing as Knuckles.
In Knuckles' storyline, a bomb is dropped near a resting Knuckles at the beginning of the game. After it explodes, the culprit reveals itself to be the lone EggRobo (often differentiated by calling it the individual "Egg Robo"). After this, Egg Robo takes Eggman's place as the level boss(Except for a retry if he dies or Flying Battery boss 2). Once Knuckles reaches Sky Sanctuary Zone, Egg Robo captures him and holds him in order for Mecha Sonic (believed to be either working with Egg Robo or commanding it) to kill him. Knuckles moves out of the way and Mecha Sonic instead destroys Egg Robo.
Egg Robo also appears in Sonic R as an unlockable character. He has abilities similar to Eggman's, though Egg Robo is slow for an unlockable character. He appears in "Sonic Adventure 2: Battle" too, as Rouge's sub kart, in the kart racing mini-game, when you get all the emblems of her missions.
Egg Robo also makes a cameo appearance on the cover of issue #11 of Archie's Sonic X comic, collapsed underneath a pile of Sonic 1-era Badniks.
The Egg Pawn army introduced in Sonic Heroes bears a more than passing resemblance to the traditional Eggrobos.