The Floating Fortress
Jump from the launch platform into the water and dive under the great naval fortress. Directly under the tower hangs a huge sinking lead, which is surrounded by a glass ball and keeps the entire construction under water. To destroy it, you need a torpedo ted from one of the nearby launchers. Swim to one of the cannons and wait until a torpedo is fired. As soon as the projectile tracks you, you swim back to the glass ball and position yourself immediately in front of it. Dodge aside at the last moment with a spin so that the torpedo bounces against the countersunk lead. The explosion dissolves the weight and the naval fortress rises a bit from the water. Meanwhile, pay attention to the bloopers and sea urchins on the seabed. If you run out of air, you can either return to the surface or collect the air bubbles that rise near the yellow propeller. There is also another cage underwater that contains a green warp tube. Behind it lies the secret green power star of this galaxy. You can already blow the tube with a second torpedo ted or focus on the regular star first.
Swim back to the surface after the destruction of the dump bleaching and jump to the yellow swimming platforms that are now arranged around the tower. On the left, the ascent begins over several narrow metal platforms. First jumps back and forth between the two walls to reach the next level with wall jumps. There you have to avoid a large stone block, which regularly drives out of the wall and can push you into the water. Wait until it is fully retracted and then jump to the opposite side. After another wall jump, you reach a section with two large stone blocks that alternately lift and lower. On the first of these blocks is already one of the five blue Star Chips that you need for the onward flight. Wait for the block to lie on the floor and jump to its top with a backflip. To do this, hold the Z key and then press the jump key. Collect the first blue Star Chip and jump back to the secure platform. Then run under the second block as soon as it moves up, and follow the path to the left. Pay attention to the water cannons and the projecting thrust walls that can push Mario off the narrow platform.
At the left end of the level, you will encounter a janitor robot who will alert you to the water cannons that have been switched on. Next to him is a large green valve. Stand on it and perform a spin to close the valve. As a result, the water cannons are switched off and a Spring Topman appears. Lures him to the circular mark on the floor and jumps to his top. The opponent catapults you upwards so that you can reach the next platform. Alternatively, the height difference can be overcome with a well-set backflip. There is a large blue screw on top, which you have to turn into the ground with a twist. This sets the upper part of the naval fortress in motion: Several platforms begin to rotate around the tower, giving you access to the remaining four Star Chips. Collect the second Star Chip on the first movable platform and then follows the rotating platforms upwards. Wait at longer intervals until the next platform has approached far enough before jumping over. Also, pay attention to the electric balls that can patrol between the platforms and push you deep when touched.
The third Star Chip can be found on a longer, fixed platform with a Goomba running around. Eliminate it with a jump or a spin and take the star piece with you. Afterwards, the moving platforms continue to a higher stone block, on the top of which lies the fourth Star Chip. Use a backflip or jump over from a neighboring platform once the block has reached a favorable position. Before you climb further up, you should collect the optional 1-Up Mushroom. This is located on the opposite side of the tower, approximately at the same height as the fourth Star Chip. Wait until one of the rotating platforms comes near you, and let it transport you to the other side. Jump over to the mushroom and then return to the moving platforms. Further up you reach a small platform with several yellow Mini Topmen and a Spring Topman. You can eliminate the smaller enemies with spins so that they do not push you from the turret. Then jump on the Spring Topman who catapults Mario far up. This is where the fifth and final Star Chip hovers. Once you have collected it, several blue Pull Stars appear above the fortress.
Climb to the highest platform and point the pointer at the first blue Pull Star. Hold the A key and pull from one star to the next until you reach the spherical planet above the naval fortress. On its surface are two electrical devices which emit red energy waves at regular intervals. Jump over the waves and run to the opposite side of the planet. There is a large golden screw on the top of one of the devices. Jump on the screw and perform a spin to turn it out. This opens up the upper half of the metallic planet and exposes a large water ball. There are numerous Star Bits and the Power Star you are looking for. Jump into the water, collect the reachable Star Bits and dip down to the center of the ball. Once you touch the Power Star, the mission is complete.
The Secret of Buoy Base
You can collect the secret green Power Star during the first mission “The Navy Fortress”. Select this mission again and jump into the water right after you land. This time, you don’t have to destroy the big lead under the tower. Instead, swim around the naval fortress to the right, looking at the seabed for a large glass cage containing a green warp tube. There are several torpedo cannons nearby, from which target-seeking torpedo teds are fired regularly. Swim in front of one of the launchers and wait until a projectile chases you. Then lure it directly to the cage with the warp tube. Once the torpedo has come close enough, you swim with a spin to the side so that the projectile hits the glass envelope. After the explosion, the warp tube is exposed. Swim to its opening and let yourself be pulled in. If you run out of air on the way, you can collect the air bubbles near the yellow propeller or return briefly to the surface.
The warp tube takes you to the bottom of the naval fortress, where a narrow path of yellow metal platforms leads along. Here you can expect several cannons that regularly fire target-seeking Bullet Bills. Run first to the left and dodge the first floor by jumping over them or dodging to the side in time. Some platforms are slightly higher than others, so you have to perform several smaller jumps on the way. Pay special attention to the abysses between the yellow areas, because if you fall into the water, you have to return again through the warp tube. There are also some? blocks on the way, from which you can get additional coins and Star Bits. If you want to collect these, you should first pass the nearest Bullet Bill cannon and find a safe position before jumping against the block. Do not stay directly in front of a launcher, otherwise the projectiles can hit you during jumping. Finally, follow the path up until you reach the large platform with the enclosed green Power Star.
The green Power Star is housed in a sturdy glass cage surrounded by several electric balls. With an ordinary spin, the shell cannot be destroyed. For this you need a Bullet Bill from one of the cannons that are located a little below the platform. Therefore, run back a bit and stand near the cannon until one of the bullets becomes aware of Mario. As soon as the Bullet Bill chases you, you turn around and run across the yellow platforms back to the star. Try to run as straight as possible and not make tight curves so that the projectile does not hit a wall or another object beforehand. You have to be especially careful on the narrow connecting platforms, because here the electric balls can injure you and cause the Bullet Bill to explosion prematurely when touched. Therefore, move past them as early as possible and guide the projectile to immediately in front of the cage. As soon as the Bullet Bill flies towards you, you jump aside at the last moment. If he hits the glass case, the cage is destroyed and the secret green Power Star is exposed. Collect him immediately to complete the mission.
This star is one of the three green Power Stars you can find in Super Mario Galaxy. The other two are at Luigi under the Saucer in the Battlerock Galaxy and the Dusty Dune Galaxy. Once you have collected all three green stars, you can activate the green Launch Star in the Comet Observatory and reach the Planet of Trials. There are three additional galaxies waiting for you with particularly difficult challenges.