EGG-HVC-001
From Sonic Retro
EGG-HVC-D01 is a large mech built by Robotnik in Sonic CD. Unlike most bosses, he only takes 3 hits. It has two large arms with bumpers on the end. A hit will take off one of the arms, and after both are off he's completely open to the final attack. It's best to hit him when he's charging up to attack. Or you could simply go to the exact right of the stage (before Robotnik appears), so you could easily hit him from behind, beating him in less than 5 seconds.