You will be entering another tank level here, which will be an autoscroller. Due to this, you will need to act quick in order to get some of the collectibles. Start off by ignoring the Blocksteppers and hopping upon the first tank. Claim the power-up from the ?-Block while defeating the Fire Bro. Get used to collecting the bombs and tossing them at the large concrete blocks, such as the one that appears on this tank. When you reach the tank with a bunch of large ?-Blocks, hit the nearby elongated one to get a bomb and toss it at those large ones. This will create a staircase of sorts, allowing you to easily reach Green Star #1.
Fight through to the next tank, which has a Fire Bro who launches fireballs over the ledge. Defeat him and hit the Red Ring for another Super Leaf, if you get all the coins. A Baddie Box will be spewing some Bob-ombs at the end of this tank, so wait to pick it up at the last second, so you can rush right and throw it at the grey brick on the smaller tank ahead – doing this reveals Green Star #2. There is a another Fire Bro on the opposite end, but you can avoid him. Continue to the next larger tank with more enemies, then use the bomb to extend the large ?-Block towards the end, allowing you to grab Green Star #3 that’s hovering in the air.
There will be a Baddie Box right at the end of this tank and you will want to hit a Bob-omb, but not pick it up right away, waiting for the last possible moment to do so. Once you do, quickly move to the final tank, go behind the green pipe and chuck the bomb at the cracked wall, revealing the Stamp. You can now enter the pipe and get ready for another encounter with Boom Boom.
BOSS - Boom Boom
Boom Boom returns from his early defeat, but he’s learned a few new tricks. On the first hit, Boom Boom is the exact same, as he will twirl around, eventually stopping after getting dizzy. On the second and third rounds, though, things will be a little different. He no longer goes invisible, instead opting to summon some shells to bounce around the room while he spins. The second round has a single shell, while the third round has two shells. They will disappear when he stops spinning and he will retreat into his shell after every hit, with nothing changing in between rounds.
Hit Boom Boom three times to win the fight, then use the Warp Box to head to the Goal Pole area.