|Bowser's Galaxy Reactor|
Right away, head forward and jump into the spotlight. It'll contort the gravity and cause you to walk on the wall that the spotlight is pointing at. Once you get up to the next platform, dodge the Dry Bones and jump over to the next spotlight. Make sure you don't hit the fire and once you head downwards, go into the next spotlight. Grab the one up if you wish when you get there and then into the next spotlight.
Once you get to the trail of star bits, you'll be free to jump down to the ledge, so do so. Go over to the right, dodge the Dry Bone and jump into the spotlight. Dodge the rotating fire and when you get to the top, head right up the stairs, dodging the Dry Bones on the way. Go into the blue light, which will send you to the next area.
Now quickly head up. The green platforms will go down into the lava, so make sure you don't stay on top of them for too long. Some of the other islands will move once you jump on top of them. The final portion of this planet is a rotating island that climaxes by dipping into the pool of water. So go in the opposite direction and then jump onto the green platform at the end. Head up and get past the fire steam and then once again go through the blue light to head to the next planet.
Here you're not able to go into the icy planet, as it'll harm you. Just follow the platforms that appear once you get close to them, just making sure you don't fall over the edge. Don't stand on one of the platforms for too long, as it'll eventually vanish. At the end go through the spotlight.
This is the desert portion of the level. Here you'll see three rotating circles, with the middle one going in a different direction than the outer ones, making it challenging to get across. Make sure you don't get hit by the fire here and continue on. Get past the rotating fire and then onto the next portion that's similar to the part in the fire level where you have to jump to the end of the rotating platforms that end in a harmful area. Make sure you go in the opposite direction, jumping over the fire. At the end jump into the spotlight.
This is another of those appearing and disappearing portions. Just head right and wall jump up here. Head to the left and then once again wall jump up here without hitting the fire. Jump into the pink gravity part of this level and continue right. Jump over the fire and then into the spotlight.
This is the last part of the level before the boss fight, and unarguably the hardest (possibly harder than the actual boss!). Basically it takes place in a huge cylinder. The challenge here are the Bullet Bills that get shot out and the Banzai Bills. The former are the more challenging, as they'll home in on you.
Right away head forward. The Bullet Bills will be shot out now, so make sure you don't get hit. Head right now and under the Thwomp, getting the coins if you need them. Now head forward once more and over the green platforms. Jump onto the rotating platforms that circle the stage, and make sure that the Bullet Bills don't hurt you. Get to the next platform by jumping onto the last rotating green platform. Make sure the Banzai Bill doesn't hit you by staying on either the right or left sides. Continue on until you get to the launch star. Go through it.
Bowser Jr. will then come in with Peach by his side. Bowser will be at the end of the flight of stairs here, so just head up them. Grab the Life Shroom and 1-Up while heading to Bowser, and make sure you do it quickly as they'll start spewing fire balls, which will destroy the stairs. Once you get to Bowser, he'll send you up to the first planet, thus starting the battle.
There are three parts here, each one requiring you to harm Bowser two times. They're each similar to the previous Bowser battles, with slight differences. On the first planet you must not get hit by the spiky plants. Bowser will start the battle by jumping up and down as usual. After that he'll form into a rock boulder, and then charge you. Before he hits you, spin attack him. He'll then start rolling around the stage on his back, so when he gets closer to you, spin attack him once more. Do this one more time and he'll then send you to the next planet.
This portion is a bit harder. Right away he'll start spewing fire balls, so dodge them. Once he gets into his shell, get behind one of the green plants. Before he gets near you, spin attack the plant so that it'll go back and hit Bowser. Do this one more time so that you'll be able to fight him on the last planet.
This one is very similar to the battles before. You want him to jump onto the blue glass so that'll he'll burn on fire. He'll jump towards you after he's finished spinning around in his shell. Do this two times and you'll beat the battle!