The Egg Mobile is the fourth boss encountered in Sonic the Hedgehog. It is fought at the end of Labyrinth Zone.
Uniquely to this Zone, rather than attack Sonic the Hedgehog with any attachment, Dr. Eggman simply uses his unmodified Egg Mobile to escape through an upward tunnel with water rising from below, thus Sonic does not need to attack him. However, it is possible to defeat him for 1,000 points; as in all other battles in the game, this requires Sonic to Spin Attack the Egg Mobile 8 times.
Contributing to the boss' challenge is that in addition to the rising water, the tunnel is filled with hazards such as Fire-Breathing Statues and moving spears that must be avoided. There are no air bubbles to be found on the way up, and if the water catches up to the player, it can be difficult to reach dry ground in time. Once the player has caught up to Eggman at the top, he will simply flee, allowing the player to destroy the Capsule and move on to Star Light Zone.
This boss returns in Sonic the Hedgehog 4: Episode I.