The Egg Kong is the fourth boss of Sonic Rivals. At the end of the Death Yard Zone, Eggman Nega (disguised as Dr. Eggman) attacks in a giant mechanical gorilla. Metal Sonic is sent to distract the player in the story.
Players must run around the Egg Kong as it fires various projectiles. Occasionally, some will stick to the ground and leave indents that the player can boost off of. Boosting on these sends a missile around the arena which freezes the first player it touches. After some time, "Eggman" will emerge from the head of the Egg Kong in a brain capsule. As he does, he fires an electric blast to the ground which sends out a shock wave that travels in both directions. This also leaves him open to attack.
Unlike the other boss fights in Story Mode, Metal Sonic can't damage the Egg Kong but there is a time limit ticking away indicating that the player has to defeat the Egg Kong within a certain amount of time.
- Unlike most of Eggman's robots, the Egg Kong is only shown with half of a body.
- Egg Kong is a parody of King Kong.
- The player's rival character tends to run in the opposite direction of the player's character most of the time in this boss fight.