Egg Mobile

From Sonic - Wiki on Neoseeker

The Egg Mobile (Egg-O-Matic in some localizations) is Dr. Robotnik's main method of travelling in the MegaDrive games. It is a small silver hovercraft, and is usually fitted with some sort of machinery, utilized for end of level boss fights. Despite Sonic continually destroying his machines, Robotnik and his Egg Mobile seem to escape unscathed the majority of the time.

Unlike the majority of his inventions, the Egg Mobile carried on into Sonic Adventure and beyond.