Firstly fly to supermassive galaxy (not on the comet level)and progress your way through until you reach the planet with the 3 huge koopas (I would reccomend a friend helping you on this because its quite hard doing it without a friend helping you,stun ONE Koopa) long jump onto its back and follow its path whilst on its back for a while you will start to see 1 ups appearing.
99 1-ups - Long jump on koopas shell
Yoshi's Infinite Flutter Glitch
Saddle on Yoshi and flutter at the last second press Z and let go of A Then let go of Z (Repeat The Steps To Gain More Height.)
Green Star Challenge
Collect all 120 stars and beat bowser and you will get a new cutscene with Rosalina reading about the green star to her "children".
Unlock Green Prankster Comets
After getting all 120 stars, beat Bowser in the final battle again. After the credits, a scene will play with Rosalina and after the cutscene, Green Prankster Comets will appear over each Galaxy.
Collect all 240 stars(Includes Normal Stars, Prankster Comet Stars, and Green Stars).
Once you get final Star from the Grandmaster Galaxy (The Perfect Run) you will be able to see your death count on your save file.
Banker Toad's Items
The toad that banks your star bits will unlocks some items as you deposit more star bits. These are not for Mario, he will simply use them himself.
||How to Unlock
||Deposit 6000 star bits
||Deposit 9000 star bits
||Deposit 1000 star bits
||Deposit 4000 star bits
|Spear and shield
||Deposit 2000 star bits
|The Perfect Run (Grandmaster Galaxy Daredevil Run)
||Deposit 9999 star bits
Yoshi Infinite Flutters
Jump holding A and before you finish Fluttering (While still holding A) Press Z, then quickly release A, then Press A again. Rinse and repeat.
Play as Luigi
Defeat Bowser at Bowser's Galaxy Generator for the first time, then check the Mail Toad for a message from him. Look for the L on the Spaceship, enter it, and then you become Luigi.
||How to Unlock
||Beat the game once.