As the name replies, Egg Scarab is based on a scarab or a dung beetle. The white on its head is where an Egg Mobile is located. Depending on the character you chose depends on the color scheme it has:
Sonic: It is mostly grey with blue parts on the arm shields, leg shields, and bottom torso. It has black spikes, and yellow arms and legs. The giant spiked ball is mostly gray with barely some black lines.
Blaze: The upper torso and the stripes on the claws are purple. It has a red bottom torso and claws, as well as gray and yellow under the torso and arms. The spiked ball is mostly gray with barely some black lines.
The battle takes place in a circular arena, in which Egg Scarab chases Sonic/Blaze rolling its spike ball around the area until it pushes the spiked ball towards Sonic/Blaze. When the ball is close towards player, he/she must hit it to reflect the ball while it is not covered in spikes to hit the Egg Scarab from behind (Egg Scarab turns around when the spiked ball is close enough to it). If the player hits the spike ball too soon, the Egg Scarab will simply catch it with its grasp. At times, Egg Scarab will fly to the middle of the circle to throw multiple spiked balls at the player. Once the battle progresses to a certain point (when the player hits the Egg Scarab about five-seven times), Egg Scarab will jump over the spiked ball to avoid being hit and the player must hit the ball again. Once hit six or eight times, Egg Scarab is defeated.
This is only non-final boss that both Sonic and Blaze fight a robot at the same time.