As the name implies, Egg Ball No.2 is a giant sphere piloted by Dr. Eggman. It is mostly gray with some black and yellow stripes on each of the sides. Both the Egg Mobile and G-merl are located by each other on an arc of the ball.
Eggman rolls around left and right on the floors, walls and ceiling in an enclosed arena similar to the Catcher Eggman in an attempt to flatten the player. While the pattern is seemingly erratic, a temporary platform can be activated by a Switch in the center of the arena, allowing the player to dodge Eggman or reach his cockpit no matter where he is (interestingly enough, Eggman can also activate this platform if he rolls over the corresponding switch). As the boss accumulates damage, it will roll faster and faster, making it more difficult to avoid and precisely attack.
After eight hits (six on Easy mode), the machine will explode and Eggman will fly away with a damaged G-merl, thus allowing the player to advance to Ocean Base.
↑ (in Japanese) ソニックアドバンス3最強攻略ガイド. Shogakukan. July 2004. ISBN 978-4091061737.