Bowser's Galaxy Reactor: The Fate of the Universe

Planet #1
The spotlights have their own gravitational pull, so stand in the light and follow it up the wall. Cross from one spotlight to the next once they're touching, but watch out for the spinning fire sticks.

After the Dry Bones, follow a few more spotlights up the tower to an anti-gravity field that'll pull you to a lava planet.

Planet #2
The platforms tumble as soon as you step on them, so you'll have to move fast. Jump from one to the next until you reach the large rotating black platform. Run along it carefully, and avoid jumping (so you don't hit a fire ball) to another set of platforms you must leap across quickly to another gravitation field.

Planet #3
The ice platforms here only appear when Mario gets close, however, unlike in Space Junk Galaxy, they'll break apart after several seconds, so time again is of the essence. Just follow the path and skip the 1-Ups unless you really need them. Another gravitational field awaits at the end.

Planet #4
Run across the three spinning platform around the flames. Watch out for another flame-set beyond (walk between the branches), then head right on the moving walkway up to some platforms, leading to another gravitational field.

Appearing Platforms
Like before, the platforms here only appear when you get close, but be careful as they'll disappear after several seconds and won't reappear, meaning what was once solid ground may now be a fall to your death.

Head right, then wall jump up the column that appears. Head left at the top, then wall-jump up a second column to a crazy gravity switching area.

Run along the ceiling past the first fire-stick, then jump to land on the walkway that appears below. Now just stay on the ground level (so avoid jumping!) and pass the fire-sticks as they swing by to reach the final gravitational field, leading to a large fiery cylinder.

Planet #5
A pair of Bullet Bill launchers ahead can make this portion difficult. Leap across the platforms when clear, but seek cover behind one of the Bowser statues for cover as soon as a bullet Bill gets close.

After crossing to the launchers, head right under a Thwomp and follow the walkway up to another set of platforms. Wait here behind a Bowser statue and wait for the Bullet Bills to cross by, then quickly leap across the platforms to one of the large floating structures and ride it around to a solid platform on the other side.

Wait to the side for the huge Bullet Bill to fly by, then quickly leap back across the floating platform to another green structure and ride it back around to the opposite side.

Leap across several more platforms and seek cover by either Bowser statue and wait for another giant Bullet Bill to fly past. Once it has, leap across three more green structures to a ledge on either side. Follow this to the Launch Star on the walkway.

Planet #6
Jump up the staircase, but don't forget to grab the power-up mushroom from a ledge on the left, halfway up.

Boss: Bowser

It's time to battle Bowser for the last time. Or should we say, the last three times. However, while there may be three parts to this battle, none of them are particularly tough.

Part 1:
Bowser will roll around in a boulder, in an effort to squash you. Avoid being run over, but perform a spin attack as soon as his exposed head is about to make contact with you. This will knock him out of the boulder and onto his back, where he'll now slide around the planet helplessly. Like in prior fights, wait for him to come back around then perform another spin attack to cause him to slide even faster in the opposite direct. Give him one more spin-attack thwack when he comes back around to enter the second portion of this battle.

Part 2:
This is almost identical to before, except now Bowser will roll around inside a spiky shell, and will launch several additional attacks, such as fireballs. However, unlike before, you can't spin attack his shell - instead, you'll have to spin attack one of the green bulb plants into him. This can be done at anytime, but is generally easier when he's standing still. After doing do, he'll slide around in his back, like usual. Spin attack when he comes sliding on to deal some pain, then repeat that once more to enter phase 3.

Part 3:
Okay, you've done this before…twice, even. Lure Bowser to drop onto any of the Blue domes when he performs his ground pound attack to ignite his tail on fire. Now run around the planet in the opposite direction as Bowser to face him head-on. When he turns around upon seeing you, spin attack his tail to send him reeling onto his back, sliding around the planet. Wait for him to come back around and spin attack him to deal some damage. Repeat this once more to best him once and for all (well, until the next Mario game, at least).