Labyrinth Zone boss

The Eggmobile is the fourth boss in the original 16-bit version of Sonic the Hedgehog, that the player will encounter in the end of Labyrinth Zone Act 3. Slightly similar boss encounter is later seen in Sonic the Hedgehog 4: Episode I, where it is featured at the Lost Labyrinth Zone. In both games, Eggmobile is piloted by Doctor Eggman.

The concept of this boss encounter is different comparing to other bosses in both games. The player does not need to hit eight times traditionally, but the encounter is more about surviving. The main goal of the boss is to the player keep chasing doctor on his Eggmobile across the very rugged and dangerous route, that has numerous obstacles from the zone, which are able to damage the player. At the same time, the water also keeps raising below, as the player can have even more difficulties to avoid obstacles and most of all, the player is able to drown. It is by consider to be one of the more challenging bosses in both games.

Sonic the Hedgehog (1991)
Eggmobile is perhaps the most unique, but also the hardest boss encounters in the 16-bit version of Sonic the Hedgehog. After the player has climb on the long upper tunnel in Labyrinth Zone Act 3, he/she will suddenly come across to Doctor Robotnik on the right of cave, who after second starts flying with his Eggmobile to the another upper tunnel. This one however is much more booby-trapped with annoying obstacles from the zone, such as moving spears and fire statues. The tunnel also is narrower and steeper as well.

Unlike the other bosses in the game, this Eggmobile is unmodified and possesses no weapons. Robotnik merely uses it to escape the flooding tunnels of the Labyrinth Zone. Sonic does not actually need to hit the Eggmobile in order to complete the zone; he merely follows Robotnik through an ascending passage with fire statues and spears, while at the same time attempting to stay ahead of the rising water. There are no Air Bubbles in this tunnel section of the zone, and if the player becomes submerged, it can be difficult to recover ground. While the player is not needed to attack into Eggmobile, if the player is skillful enough, the player is able to make Eggmobile exploding after hitting eight times to it. In Sonic Mega Collection Plus port of the game, the player is only have to hit three times to make Eggmobile exploding.

Once the player reaches the top of the passage, Robotnik will fly away. After opening the capsule, the player heads to the next zone.

Sonic the Hedgehog 4
The encounter of the Eggmobile is later seen again as a third boss in Sonic the Hedgehog 4: Episode 1, that the player will face at Lost Labyrinth Zone. At the start of the boss act, the player has to pick up some rings and head to the Doctor Eggman, who after laughing, starts fly away to the route at the right. The route is more wheeling and smoother than before. However like in previous game, there are also numerous booby-trapped obstacles like spears, but there are also badniks as well on the way. Despite the smoother platforming sections, the water once again rises below, while like in original Sonic the Hedgehog, there are no Air Bubbles on the route, as the player has to pass quickly as possible without drowning. The player is able to attack Eggmobile by doing Homing Attack into him.

After bounced to the air by Spring, the player chases Eggman on the linear arena until the second phase of the boss battle starts on and where the things start getting different. Eggman summon two pillars rise from the ground enclosing him and Eggman. He then summons numerous different looking pillars slowly as attempting to crush the player, while the doctor himself flees to the safer place. The player has to head to the same place as well to survive and manage to hit once Eggman at the same time. Eggman repeat doing this with different pattern until the player has defeated him, who also should memorize patterns, in which an opening appears.

After doing four hits into Eggmobile, all pillars disappear around the arena, while Eggman flees away with damaged Eggmobile and the player is also able to open the capsule and complete the zone. This battle later reappears at E.G.G. Station Zone as a part of the boss rush before the final boss. While the chase section is not included, it moves to the newer part of the battle, where all pillar patterns are similar, but accident design of them is replaced with high-tech ones to fit space-themed zone. After another four hits, all pillars disappear and the player can move to the next boss.

Trivia

 * Before the player face Robotnik in original Sonic the Hedgehog, the Shield monitor is seen on left side of the cave, which can be helpful during the chase.
 * Strangely, in the iPod (click wheel) port of the original Sonic the Hedgehog, a glitch causes the water to stop rising at a certain point, making the chase significantly easier.
 * The boss encounter is more of a psychological boss than a physical one. It is not too easy to drown in, even if the player takes their time.
 * During the second phase in Sonic the Hedgehog 4, the way the block pillars rise from the ground and the way Sonic has to stand on something to reach Dr. Robotnik is similar to the Hammer Eggman boss of the Aquatic Ruin Zone in Sonic the Hedgehog 2.
 * In Sonic the Hedgehog 4, it is possible to hit Eggman before the battle really starts, standing on one of the walls that rise at the beginning of the battle and do Homing Attack into him in the quick second. It is also possible to do it in E.G.G. Station Zone.