Great Eggman Robo

The Great Eggman Robo, known in Japan as the Kyodai Eggman Robo, was a massive battle robot that served as the final boss of the Death Egg Zone in Sonic's or Tails' story of Sonic & Knuckles, as well as its locked-on form, Sonic 3 and Knuckles. Powered by the Master Emerald, it was used by Doctor Eggman aboard his damaged space station.

It somewhat resembles the Death Egg Robot, which is the final boss of Sonic the Hedgehog 2, only this robot is much bigger and has a better resemblance to EggRobo.

This enormous mech is fought in three phases. Like in the final bosses in Sonic 1 and Sonic 2, there are no rings in this final boss (not counting the Doomsday Zone), 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.

Phase 1
In first phase, Sonic has to destroy all of the machines 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.

Phase 2
In this second phase, Sonic must avoid the flaming snot 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 Emerald compartment and fire its primary weapon. 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.

Phase 3
As the Great Eggman Robo falls apart, Dr. Robotnik manages to detach his Eggmobile with the Master Emerald in tow. With the Death Egg exploding all around him, he puts up one last effort to keep the omnipotent jewel from Sonic. The player has to hit Eggmobile normally 8 times to be stopped.

All there is to this phase is running to catch up with the Eggmobile 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 3 and Knuckles, you fall back to earth with the Master Emerald.

Trivia

 * This boss stage is not available for Knuckles unless a cheat is used.
 * The music for this boss battle is the same for the final boss of Sonic the Hedgehog 3.
 * 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.
 * The Great Eggman Robo is very likely to have been inspired by the Giant Warrior from Hayao Miyazaki's movie 'Nausicaa of the Valley of the Wind'. The resemblance is particularly noticeable in that both can fire giant laser beams from their mouths, to extremely lethal effect.
 * In DLC track of Sonic and Sega All Stars Racing, several laser turrets resembling the Great Eggman Robo appear in the hangar area of the Death Egg.