It can only be found at Knuckles the Echidna's story in the action stage Casinopolis. It looks like the generic pirate puppet with light green (or blue) and white clothing, but it does also have a sword as its weapon.
Egg Pirates can be found running in circles on the ships above the main lobby of Casinopolis. When defeated, instead of dropping an animal as most robots usually do, it drops rings for Knuckles to collect. The other E-series robot E-22 Beat has this gimmick as well as they are the only robots in Sonic Adventure that are not powered by an organic battery.
A E-29 Egg Pirate found pacing along one of the Ships Yards is Designed differently, looking like a captain. This Egg Pirate moves faster making it more dangerous, It does however, slow down when turning, allowing Knuckles to set up a punch as it comes towards him.