Submarine Eggman (サブマリンエッグマン,Sabumarinegguman?) is the fifth boss in Sonic the Hedgehog 2. The player encounters Submarine Eggman at the end of Hill Top Zone Act 2 and it takes eight hits to defeat. This floating submarine is piloted by Dr. Robotnik.
Despite having the name "Submarine Eggman", it travels through lava instead of water. It resembles the Egg Mobile with a gun mounted on top. Being mostly grey, it has black and yellow stripes and orange headlights.
The boss battle takes place on three small pieces of land with lava in between each of them. Dr. Robotnik begins the battle by rising up from the lava lake on the right side. This Egg Mobile has a nozzle at the top, which starts to shoot fire once. After Dr. Robotnik shoots, he submerges back into the lava. Before Egg Mobile submerges fully, two fireballs come out of the lava and onto the land, temporarily setting the land on fire. Dr. Robotnik returns within a few seconds to either the left side of the arena or the same spot where it sank before. The Egg Mobile then proceeds to repeat the attack pattern until it is defeated.
Like the other Egg Mobiles in Sonic the Hedgehog 2, Submarine Eggman takes eight hits to be defeated. After that, the player has to be careful not to fall into the lava after defeating the boss and head to the capsule.
The player is able to keep hitting the Egg Mobile for all eight hits to destroy it faster. However, the player may also fall into the lava after defeating it and can either lose a shield, rings or even a life.
Strangely, this boss does not appear in its zone in the 2013 iOS re-release version 3.0.0, having been replaced by a Goal Plate. It appears in its Android counterpart normally and it has been addressed in version 3.0.1. The boss does, however, appear in the boss rush zone.