- This boss is from Sonic Rivals. You may be looking for Egg Turtle (Sonic Rush).
It is a gigantic robotic turtle with orange feet with a stripe of white in the center. Its shell is colored in green with silver lines around it. The head is also orange with two red eyes, a strip of white going through the center of the head up to the glass where Eggman's cockpit is located and the head is connected to the shell by a few large metal rods.
The battle takes place upon a circular field. Players will run around the field as the head of the turtle rotates around. At random instances, it will stop and pop out both its head and its tail. Jumping on the head gains the player a hit, while jumping on the tail sends out a shockwave that will damage the player's rival. (Beware that this shockwave can also damage the character who hits the tail in the first place.) As it takes several hits, the Egg Turtle will spin faster and even while sticking out its head and tail it will continue to rotate around the stage
The first player to accumulate six hits wins the battle, and the boss is destroyed.