Collect all 120 Stars. Then, go to Rosalina on the Comet Observatory, and request to fight Bowser again. Defeat Bowser to view an alternate ending. Once the credits finish, you will get a message saying Luigi is now playable. Luigi is just like Mario, but he jumps higher, runs faster, and has lower traction.
Collect all 120 Stars with Luigi, and defeat Bowser to unlock the Grand Finale Galaxy for both Mario and Luigi, which is the Star Festival seen in the beginning of the game.
Collect 100 Purple Coins in the Grand Finale Galaxy to get the final Star.
Collect 9,999 Star Bits in the Hub to change all coconuts in the game to watermelons.
Collect the final star in the Grand Finale Galaxy with both Mario and Luigi. The information from your saved game file will now include the number of times you lost a life.
To get flying Mario, you need to get the sixth Grand Star that will open two new domes, "The Garden" and "The Gate". Enter "The Gate" dome, and talk to the red Luma that gives you a challenge to get all 100 purple coins. He will give you a red star that makes you fly after you spin in midair. After finishing that challenge, the same red stars will appear in the observatory to make Mario fly.
To jump even higher than a triple jump, first do a triple jump. At the peak of your third jump, spin. This will make you jump higher so you can reach things that are too high to reach with a triple jump.
Spin in mid-air, then immediately press Z to hit the nearest target.
Note: For a better effect, do the following at a high angle. Jump and spin. As soon as you see the light, ground pound. Mario will do a cannonball, then slam on his legs with his hands in the air. This is more powerful than a normal spin.
While playing the game, use a second Wii-mote. Although a second player will not appear, the second Wii-mote will have its own pointer, allowing another player to assist by collecting items and helping Mario's jumps.
Allow the game to idle for approximately one minute, and Mario will go to sleep.
Go to where Polara and Rosalina stand together by the beacon. Stand far enough away from Rosalina so that the talk sign does not appear. Then, try to jump on Rosalina. A bubble will form around her.
Go to the room where Rosalina is standing. Zoom in, aim at her, and press B to fire a Star Bit at her. When it hits her she will jump because it scares her, and it will hurt her.
Perform a long jump (press Z then A while running) towards the Beacon (the big yellow ball off the platform where Rosalina is standing). If timed correctly, you will land under the Beacon without being carried away until you slide further away from the Beacon.
Note: You must have the Engine Room dome unlocked. Go outside of the dome. Move slightly to the left, then jump off the platform, and slide down the curtain. After falling off the curtain, immediately Ground Pound and fall into space. A bubble will carry Mario or Luigi back up to the Engine Room. While he is going up, the screen will flip for about two seconds. Note: This may not work every time.
As you are running up the stairs to fight Bowser for the final time, collect the 6 Life Mushroom and Life Shroom. You will first be on a sphere with spiky plants. Bowser will roll into a brick ball and chase you. When he is nearby, spin. Do this two times. Next, you will be at a rock with little plant things. He will breathe fire. Protect yourself by hiding behind the plant things. He will then curl up into his spiky shell and come at you fast. When he is close, hit the plant thing at him. Do this until you are at where you usually fight Bowser. Make him ground pound the glass and burn his tail. Hit him once, then hit him again when he is on his back. The last time you do this he will spin very fast. Time it, then hit him.
Above the tower where you collect the Blue Star Pieces is a little planetoid that is a sphere with two red panels on top and a lighter bottom with a screw in the middle. It looks exactly like a Pokeball.
At the Comet Observatory, run around and collect the 1-Up Mushrooms. Then, go into a Dome, come back out, and all the 1-Up Mushrooms will have respawned. Note: More 1-Up Mushrooms can be collected after you unlock the Red Star.
You can use the cannon on the beach for a shortcut. Normally you would need to use the cannon to shoot yourself to the nearby planet to get a Fire Flower then use the Jump Star to return to the beach so that you can light the two torches to open the door on the first Star, or the three torches to make the Ice Flower appear on the second Star. However, if you get in the cannon and turn it all the way to the left as far as it will go, you will see two yellow platforms moving up and down. Watch them carefully. When the farthest platform is up, line your crosshairs up with the side of it. Then, wait until the closest platform goes back up, and fire yourself in that direction. If timed correctly, the platforms will have switched again and you will hit the side of the furthest platform and fall on the ground. You must hit the wall or you will overshoot and die. This will put you inside the "bowel" area without opening the door on the first Star. If you are on the second Star, you will not have to worry about getting the Ice Flower to cross the lake and jump the faucets. You can just proceed right and climb the poles to get to the Bubble Shooter.
This Star is difficult to get because the bombs do not seem to explode fast enough. First, place a bomb on all of the little yellow circles that you shoot to make a coin. This will provide the best blast coverage, so you will need six bombs. When the level starts, long jump the left-most bomb. Take it, run forward a bit, and throw it at the furthest left side yellow dot. Next, long jump back to the second bomb (from the left), and take that bomb. Turn around, and throw it. The bomb should land just about on the left side middle dot. Get the third bomb, and do the same thing. It should land just about on the right side middle dot. Next, take the fourth bomb, and run forward a bit. Throw it at the furthest right side dot. Long jump back to the first bomb again. It should be just barely shooting out another bomb. Take it, and throw it at the closest left side dot. Finally, get the second bomb (from the left), and toss it at the closest right side dot. When you pick up that last bomb, you should have about fourteen seconds remaining on the clock, and must have at least eleven seconds. It is important to take the second bomb for the closest right side dot because it lights when you pick it up. The bomb will already be active while you run to the dot. It is also important to get the bombs as close to the yellow dots as possible and execute all your moves flawlessly (no unnecessary jumps or spins) as every second counts. This will require some practice. You must experiment with how far Mario can throw the bombs. For the left and right furthest dots, try throwing them when you are even with the closest dots.
Before the race begins, hold Forward. Press Z to crouch when the timer reaches "2", then immediately press A when the race begins. If done correctly, Mario will turn yellow briefly and get a quicker start.
When racing against Cosmic Mario, perform long jumps to reach the goal quicker.
There is a comet where there are a lot of Star Bits. Grab onto the nearest grey tree, and collect all the Star Bits. You will get an extra life because of the number of Star Bits. Once you have collected all of the Star Bits, intentionally fall into the black hole. You will not lose a life because of the previously awarded extra life. After you have jumped into the black hole, you will respawn at the last grey tree you were on. Collect all the Star Bit again, and jump off. Continue doing this to get as many Star Bits as desired. Each time will result in about fifty Star Bits.
Select the Tarantox's Tangled Web Star. Play through the level until you get to the glass-covered planet. If you have not already done so, feed the Hungry Luma fifty Star Bits. Use the Launch Star it creates to go to the Yoshi head planet. Then, without killing them, collect as many Goombas as possible, and get them to follow you. You will need at least eight of them. Jump and keep bouncing on them without hitting the ground. A number should appear that counts up to "7". On the eighth Goomba, you will start getting extra lives for every Goomba you bounce on. It is possible to get more than ten extra lives per attempt.
One of the planets is shaped like Captain Olimar's rocket ship that appeared in Pikmin and Pikmin 2.
At the main menu, hold 1 + 2 and press A + B to access two hidden stages.