|Bowser Jr.'s Airship Armada|
Now go forward, dodging the enemies. If you need a coin, shoot the gold thing jutting out of the ground then continue on through the cannon. Shoot to the pull star and head down. If you have thirty star bits, you can pay the hungry Luma for a Life Shroom. If not, then you can find some more star bits by searching this airship. Anyway, go forward, dodge the Mandibug and hit the switch by spinning.
This will cause the platform you're on to start and move. Dodge all of the bombs that are launched and get the 1-Up if you want to. If you get hit by a bomb, then it's highly possible that you'll fall off of the platform, thus getting rid of a life. Jump the bombs if you need to! Anyway, either kill or dodge the spider that comes up. At the very end of this, you'll have to dodge or attack a row of three spiders.
Now head up the bridge and get past the Magikoopa. Use the sling star to get on top of this airship, which will cause the boss fight against Bowser Jr. to start. Bowser Jr. will fight in his airship, and will summon all sorts of enemies including Bullet Bills, cannons, Koopa Troopas, Magikoopas and fiery balls.
Anyway, to harm Bowser Jr.'s airship, find one of the Koopa Troopas and grab its shell. Now face the airship, jump and then launch the shell at the ship. After doing this three times (note: Each time you hit him, the battle will get harder) he'll spin his ship around and a large face sculpture of Bowser will be looking at you. This portion of the battle is much harder. Not only will he send out more ammunition, though it's a smaller target as well. Throw two more shells at him to ultimately win this level, then collect the grand star. (Note: During the battle, if you like, you can shoot a star bit at him and several Star Bits will pop out of him; grab these if you need them, but you can only do this once.)