Super Mario Galaxy 2/Grandmaster Galaxy

The Grandmaster Galaxy is the last and final galaxy in the Super Mario Galaxy 2 game, and to be able to open it and to get the last 2 stars, it requires certain conditions.

Requirment
To be able to take the ultimate test in the Grandmaster Galaxy, you gonna have to collect all the stars available in the game. Only once you will have 240 stars (120 Gold stars and 120 Green stars) this Galaxy will show up with The Ultimate Test level.

Requirement
While activating the first level might be "easy", to activate the prankster comet star, you will have to gain 9,999 star bits in Toad bank account. There's no easy way to gain all of those except for grinding levels, or replaying the game in new save and sending star bits in toad bank to share the bits. Once you gather all 9,999 star bits, the level will show up.

100% Completion
Once you gain all 242 stars, there will be an addition to Mario starship - Rosalina. Talk to her and she will thank you for gathering all the stars in the game.

Also, in the main save screen, your icon will shine with sparkles, and the title for your save will get a crown and the title will be "Master of Galaxies!". Congratulation on finishing the game 100%.