I'm starting to get tired of people asking this question.
You have to complete a Castle or buy something with your Starcoins to save. i no its pretty rubbish x ;)
You have to complete the world five castle as mini mario.
every time you complete a dark castle or spend 5 starcoins to get a mushroom you can save the game.
you cant(n)
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Complete w7-6
you get to the world 7 by beating the world 5 final boss witha mini mushroom
beat bowser castle after the ship
complete all the levels duuh
You walk, and complete the stuff before it.
complete S-Bowser Castle
Complete the game as Mario, then press Select on the World Map.