Kyodai Eggman Robo (巨大エッグマンロボ Kyodai Egguman Robo?, lit. "Gigantic Eggman Robo") was a massive battle robot that served as the final boss of the Death Egg Zone in Sonic's story of Sonic & Knuckles, as well as Sonic's and Tails' story in its locked-on form, Sonic the Hedgehog 3 & Knuckles. Powered by the Master Emerald, it was used by Dr. Robotnik aboard his damaged space station.
This enormous mech is fought in three phases. Like in the final bosses in the original Sonic the Hedgehog and Sonic the Hedgehog 2, there are no rings in this final boss, although any rings still in hand from Act 2 are carried forward, so the first attempt at this boss may actually be the player's best chance of succeeding.
In first phase, Sonic has to destroy all of the machine's fingers while dodging them trying to crush him. To do this, he must either do his super spin dash between them, positioned as in the picture just as the fingers are about to slam down, or jump on each one. Three hits are needed to destroy each of the six fingers.
In the second phase, Sonic must avoid the flames fired from the robot's nose. This is lethal right from the moment it leaves the nose, meaning the player has to time attacks very carefully, as the nose is the part that needs to be hit.
Hitting the nose will not cause any damage, but will trigger the mech to open its primary weapon chamber, where it stored the Master Emerald as its power source. This is a magnifying glass that is capable of channeling energy from the Master Emerald into a huge laser beam. The player can score a hit (or two) by hitting this area while the weapon is charging. To defeat this phase, player has to hit it 8 times.
Just as the weapon is about to fire, the player needs to either head as far right as possible and then duck, or jump at the right moment. It is best to listen to the sound the weapon makes as it charges to help with the timing with dodging this attack. A split-second after the sound goes off, the weapon fires.
Another good way to avoid contact with the laser beam is to jump over to the left and hit the top of the Emerald compartment right when the laser beam is fired. It's recommended not to try and hit it again right after this, as the Emerald compartment might close on you and cause you to fall off the bottom of the screen.
As Kyodai Eggman Robo falls apart, Dr. Robotnik manages to detach his Egg Mobile with the Master Emerald in tow. With the Death Egg exploding all around him, he puts up one last effort to keep the mighty jewel from Sonic. The player has to hit Egg Mobile normally eight times to be stopped.
All there is to this phase is running to catch up with the Egg Mobile and hitting it eight times. The floor rapidly drops away during this part - nearly as quickly as Sonic can run. The biggest danger is flying off the end just after the last hit is scored, making for an extremely frustrating death. Keep holding right down especially after the seventh hit to avoid this pitfall.
After this boss fight if you have collected all the Emeralds via Special Stage, you advance to The Doomsday Zone to fight the true final boss. If not, then you fall back to Earth and the credits roll. If you're playing as Tails alone via playing Sonic the Hedgehog 3 & Knuckles, you fall back to earth with the Master Emerald.
- Only the upper part of the robot's body is ever visible; the lower body, legs, and arms are never shown.
- This boss segment was settled in Sound Test as The Doomsday Zone: Act 2
- This boss stage is not available for Knuckles unless a cheat is used. When Knuckles does fight the boss, although Robotnik can be seen entering the robot, EggRobo is seen retreating with the Master Emerald in the third phase of the battle.
- The right eye of this robot is different than the left one. It can be used by Robotnik as a pointer or it can be the Egg Robo assisting him in controlling the machine.
- The music for this boss battle is the same for the final boss of Sonic the Hedgehog 3.
- In DLC track of Sonic & Sega All-Stars Racing and Sonic & All-Stars Racing Transformed, several laser turret droids resembling th Kyodai Eggman Robo appear in the hangar area of the Death Egg.
- If Sonic & Knuckles is played on Sonic Classic Collection, then it is possible to save up to this point without having to do the entire zone again.
- If the player dies after engaging in combat with this boss battle, when they re-enter the battle, their time will be completely reset.