Bowser Jr.'s Boomsday Machine
- First planet
You start out on a little planet with broken robot pieces littering it and sticky mud everywhere. When you get close to the cannons, Bullet Bills will start shooting out and if you're close enough they'll chase you. You need to lead a Bullet Bill across the first mud strip and over to the glass cage on the other side past the Fizzlits, where you can jump up and let it crash the cage for you. There is also a Chance Cube on the side of the planet behind the cannons. After you break the cage, jump into the square hole and fire Mario off to the next planet by aiming the crosshairs and firing with . If you want, you can hit one of the Boomerang Bros. on the edge of the next planet, but you get a 1-Up for hitting the center of the target on the side. To hit the center, aim slightly above the bullseye in the center.
- Second planet
Facing the Boomerang Bros., just wait until they've thrown two boomerangs, then jump on top of them and either jump on them again for a coin or run into them for Star Bits. Watch out for their boomerangs, which return even after you killed them. When you kill them both a Launch Star will appear in the middle of the area. Before you go, climb up the flagpole diagonally across from where the target to get a Life Mushroom. The Launch Star will take you up to a small planetoid with a checkpoint flag and another cannon you can shoot out of. Just wait for the mines that are circling to pass in front of you and aim for the target at the bottom of the planet, where you can score another 1-Up for hitting a bullseye.
- Third planet
From the platform where you land, jump out onto one of the circling red platforms and from there jump to the circling blue platforms. Stay on the top or bottom edge of the blue platforms to avoid the mines and let them take you around so you can get a Cloud Flower and the Comet Medal. When you have a Cloud Flower, jump off to the platform above you, making clouds to get up there. At the top is a stack of breakable stone discs surrounded by mines. Ground pound the stack of stones to create a Launch Star that will take you to the boss planet.
- Bowser Jr.
Bowser Jr.'s Boomsday Machine is a tall tower in the center of the planet that spins fire wheels along the ground as it moves. You need to use your clouds to get up to the top of the machine and ground pound the glass enclosure where Bowser Jr. is sitting. Along with the fire wheels, the machine also spits out electric orbs at you that will hurt you and destroy your clouds. There are plenty of Cloud Flowers around the planet and grates that blow air up so you can get some elevation to high enough.
Start out by backflipping and spinning on one of the air grates to go up to the cloud at the top and grab the Cloud Flower up there to replenish your stock. If you're about to be hit by an orb, just jump and spin to create another cloud. At the permanent cloud up there, long jump and create clouds over to the top of the machine. Don't waste time while you're on top of the Doomsday Machine, because it will spin you off. As soon as you're over it, jump and ground pound to crack the glass. In the next round, the machine will add an attack where it sucks the air into itself, pulling you over to it if you're on a cloud and another attack where it electrifies so you can't ground pound it. Use the same strategy to get up to one of the permanent clouds, then long jump over to the machine and ground pound the glass again, making sure to wait until it's not electrified. Don't worry about creating clouds to stay above it while you wait; you can ground pound right through them.
After injuring the machine twice, it upgrades into an even taller tower with tank tracks that let it move around the planet. Now you can also die by crushed by the tracks or being pushed off the planet. Now when you get to the top of one of the air grates, you'll want to start jumping and making clouds to get up higher to the next set of permanent clouds with Cloud Flowers on them. Up there you can replenish your stock and long jump over to the top of the tower like before. You'll have to wait until the machine isn't electrified, but this time you'll also need to stay over the tower as it moves around the planet. Ground it pound it one more time to defeat the Bowser Jr. and get your Grand Star.
Boomsday Machine Daredevil Run (Prankster Comet)
This is a modified version of the previous star, except you only have one health the entire time. The first planet is the same, minus the coins, so lead a Bullet Bill over to the cage and destroy it. Next shoot yourself up to the fight with the Hammer Bros., then take the Launch Star up to the planetoid with the checkpoint and another cannon. This part is a little different, as now you need to shoot Mario down to a moving platform on the next planet. If you aim in the middle of its path you can't miss, but if you hit the center you can get a 1-Up. Take the walkway off the top of the platform and follow it around past a Dry Bones to another platform. When you get on it, you'll need to run across it as it tips back and forth so you don't fall into the antimatter. At the end you can jump off and hit another checkpoint and grab a Cloud Flower. Use your clouds to get out to the Launch Star, optionally grabbing the 1-Up Mushroom on the right as you go. This takes you to the boss fight with Bowser Jr. and his Boomsday Machine, which is exactly the same as before, only you can't take any damage.
Both Green Stars are very easy to get, as all you have to do is shoot yourself out of a cannon at them. The first Green Star should be easy to spot—it's right above the target you shoot at from the first cannon. The second Green Star is all the way to the left when you're shooting from the second cannon after beating the Boomerang Bros.