During gameplay use a second Wiimote and although a second player will not appear the second Wiimote will have it's own pointer giving the other player the ability to assist in collecting items and helping Mario's jumps.
Watermelons instead of Coconuts:
This will happen when you have collected 9,999 Star Bits in the Hub.
Fly with Mario:
When you have beaten Bowser with Mario go to the gate and step onto the little castle. Agree to help Rosilina protector of the cosmos and she will leave you with a red powerup luma to help you. Collect ALL 100 purple coins and you will get a red star which will give Mario red and black clothing and the ability to fly.
When you have collected the final star with Mario and Luigi so you have the required 120 to unlock the 'Grand Finale Galaxy' and saved the game you can then view your death count on your 'Save' file to see how many times you were killed during the game with Mario and Luigi.
Starting Boost when Racing Shadow Mario:
When you are racing against Shadow Mario hold forward when the countdown timer starts and when it hits 2 hold down on Z to crouch. Then press A as soon as the race starts and for several seconds you will turn yellow and recieve a boost that will leave Shadow Mario way behind.
To perform this special move which attacks the nearest enemy or breakable object in the game you have to press Z when you spin in midair.
Unlock Grand Finale Galaxy and Star 121:
Collect ALL 120 stars with Luigi and beat Bowser, when you've done this the Grand Finale Galaxy becomes unlocked which is the Star Festival you saw at the start of the game. When you have collected the 100 purple coins in this galaxy you get Star 121 which is the final star.
To unlock this hidden character you must collect ALL 120 stars and then return to Rosalina on the Comet Observatory and ask to fight Bowser again. When the credits have completed you will see a message that tells you that Luigi is now available as a playable character.
Get the star by the Garage that makes you fly.Fly to the top of the Garden and at the point there is an Up Mushroom.Also under the Gate is an Up Mushroom!
Good Egg Galaxy shortcuts:
Where the luma says he'll become a sling star to bring you to the launch star, you can also backwards somersault to the launch star.
Instead of entering the house, you can backwards somersault to the roof.
On the big star with blue star chips, you don't need to get any star chips, you can long jump to the star.
GLITCH ON GRAVITY:
Go to Dreadnought Galaxy, Star 2 (Dreadnought's Colossal Cannons), get to the checkpoint before you start the platforms and avoiding cannons. Then, when you jump to go on the upside-down platform, don't TOUCH IT, just go in between the small platform and the moving one. Your character will fall through, but not die because gravity keeps changing, stopping him from falling. WARNING: I cannot find a way out of it, so you will have to retry the level.
In the observatory grounds use the red star which enables you to fly(unlock gate first and do red luma request). Then fly towards the gate and underneath is a one-up.
3rd green star!:
Okay. Go to the dusty dune galaxy and go to the 2nd star. After you go through the first launch star go to the bottom of the planet. The hungry luma will want 20 star bits. Feed him and he will transform into a pyramid planet. Collect all five silver stars inside of it and the green star will spawn at the bottom.