Welcome to the first autoscroller of the game, meaning that the level will move along on its own and once you pass things, you won’t be able to backtrack. You will be moving along tanks here, so you will want to keep up with things, although the camera angle kind of makes it hard to get too far ahead. On the first tank, you will find some ?-Blocks, one of which will yield a power-up. Continue to the second tank, watching out for the Bullet Bills being launch from it. When you get to the second set of ?-Blocks, one of them will turn into a Cannon Box.
Fitting over your character’s head, the Cannon Box will automatically fire cannonballs, but you can hold down the Y/X buttons to charge it up, having the shots go farther. Hit the Red Ring a little ahead and if you get all the coins, you’ll receive another Fire Flower. Ahead is another chance to get a Cannon Box by breaking the Bullet Bill Cannon. After the first wave of tanks, you’ll get a chance to defeat some Piranha Plants that guard Green Star #1 – note that you can shoot the star to collect it.
Keep going and when you see a small tank with a single wooden crate on it, break it open to collect Green Star #2. When you reach the tank with a cage on it, quickly climb to the top of it to retrieve the Stamp. You will be close to the end at this point and if you still have the Cannon Box, good, as you will need it. The pipe at the end will take you to the next bit, but don’t dive into it just yet. You should see a cracked wall beyond the pipe, with Bowser’s icon on it. If you have the Cannon Box, shoot the wall until it breaks, revealing Green Star #3. Jump into the pipe to face a boss now.
Boss: Boom Boom
Boom Boom spins around the room, but it’s simple enough to jump on his head. If you don’t feel safe doing this, avoid Boom Boom until he stops, making it a lot easier to jump on his head. Doing this causes him to slip into his turtle shell and bounce around the room. You can’t do anything about Boom Boom while he’s in his shell, so just dodge him. On the second and third hits, Boom Boom will turn invisible while both spinning and his his shell, although there is a slight hint of his outline. Hit him three times to defeat Boom Boom.
Upon dealing the final hit against Boom Boom, a Warp Box will appear, bringing you to the Goal Pole. Do your thing here to rescue the Sprixie Princess and gain access to World 3.