The Egg Hammer Tank (エッグ ハンマー タンク Eggu Hanmā Tanku) is the first boss in Sonic Advance, which takes place in Neo Green Hill Zone. Dr. Eggman appears on his Eggpod and flies away, then, Egg Hammer Tank appears. It's a tank with a giant hammer attached.
Basically, the player must hit the cockpit eight times (or six if in easy mode) to defeat him, while he drives left and right across the bridge. They must take care of the hammer as it swings back and forth, and at the seventh hit (or fifth if in Easy mode), he will use the hammer to make the vehicle jump very quickly.
Surprisingly enough, Amy (who lacks the ability to go into ball form in this game unless forced into it) has the easiest time beating this boss thanks to her mid-air Hammer Whirl attack ( + ), which allows her to continuously bounce off of the mech as it slowly rolls along in a more controllable fashion than bouncing off of it with Sonic's/Tails'/Knuckles' jump attacks. By doing this, she can easily get the boss down to its final hit before it goes off screen for the first time.