Rexon

You may be looking for Rexxon. Rexon, known as Zaura (ザウラ) in Japan, was a second-generation Badnik created by Dr. Robotnik in Sonic the Hedgehog 2 for the Sega Genesis.

Physical Appearance
A Rexon resides in molten hot lava, its armored carapace meant to withstand the immense heat of its domain. Its backside (or shell) is indestructible and can be used as a platform, but when an enemy comes near, the head and neck retract from their safe home to spot intruders. Their necks are not 100% stable, so it sways back and forth while they search around. Their plating is light purple and pale blue. The appearance of this Badnik is based on plesiosaurs, according to pictures in the game manuals. When they are destroyed the head and neck detach and are destroyed, leaving only the shell behind.

Attack Pattern
The Rexon retracts into its shell until its sensors indicate an enemy presence. When a target is spotted their neck and head retracts and floats above the surface. Internal heat mechanisms then allow the Rexon to spew dangerous fireballs from their mouths periodically. Despite their intimidating appearance, Sonic found ways to exploit their platform-like shells as a stepping stone to beating them.

Sonic SatAM
Rexon appeared in the episode "Ultra Sonic" it was called a Dinobot which it does not shoot fire out of it mouth, instead it shoot a laser from it nose.

Trivia

 * In Sonic Spinball, a similar but larger robot named Rexxon appears in the Toxic Caves.
 * In Sonic Blast, an unnamed badnik based on Rexon appears in Red Volcano Zone.
 * Rexon appears in Sonic and the Black Knight in winning Fan Art.