Well, if you are talking about New Super Mario Bros. for DS, you go the final castle in world 5 where you fight Petey Pirhana. Well, the thing is that you need to defeat him WHILE you are mini Mario or Luigi.
All i know is that the mini mushrooms are in world 2 boss castle(to unlock world4) and world 5 boss castle(to unlock world 7) you have to beat the worlds 2 &7 boss when your mini Mario, in order to unlock worlds 4 & 7, it will be a little difficult beating the bosses when your mini Mario but it's worth it
First go to the world 3 last castle or world 6 last casltle if you are mini mario, then you beat bowser there is a little hole and it leads you to world 4 and 7.
you have to get a cannon from one of the worlds and go in it and boom your there
Ok Hi Well first you have to complete the world 6. Then you go to world eight. Then you must complete the HU-MON-GUS castle at the end. It's quite difficult. But anyway, if you do that (WELL DONE IF YOU DO, I had to get my brother to do it for me) You'll get world 7 and 4 (if you haven't unlocked that.) OR you have to complete the castle in world 6 as mini mario, and that's really hard. Bye! You don't get world 4 and 7 automatically when you finish the game. You have to beat the world 2 castle as Mini Mario to get world 4 and you do the the same except to world 5 to get world 7. World 4 is jungle themed and world 7 is sky themed. Have fun!
Visit the castle in world 2 or 5, find a mini mushroom in a ? block or use it if you have it as an item to fight the bosses. You must defeat the bosses in world 3-castle and 6-castle as mini mario (or luigi). After collecting the key and adding your bonus, the gate on the right side will open up. If you'd done the castle before as regular mario or luigi, you'll see your character question why peach isn't there. If this is your first time completing the castle and you defeat the boss as mini mario or luigi, your character will see bowser jr. making noises at the character and running off while your character falls into a little hole and turns the sign when he gets near from "W3" to "W4" or "W6" to "W7." If you'd done the castle before as regular mario or luigi and you want to unlock world 4 or 7, defeat the boss as mini mario or luigi. This time, your character will question why peach and bowser jr. aren't there. And he will fall into the little hole and change the sign as stated above. Then you will unlock world 4 or 7 and get an opportunity to get big in the first world of 4 or 7.
To get to world 4 you need to beat the world two castle as Mini Mario To get to world 7 you need to beat the world five castle as Mini Mario
you have to complete the last castle on world 5 as mini Mario :) have fun !
you have to defeat the boss in world 5 castle with mini mario.
For world 4 complete world 2 castle defeat the white thing being mini Mario and for world 7 do the same except on world 5 castle!
To get World 2, just finish the World 1 castle course; to unlock World 7, finish World 5 castle course with MINI MARIO (this is important)
In super mario? Ahem... You do all of the tasks before it.
you have to pass second castle So Easy BY JAKEALDERMAN
here's a cheat: you can do a barrel roll.
Get a red flag on the levl before the world 7 castle
you beat the world 5 castle being tiny.
You have to complete the world five castle as mini mario.
All i know is that the mini mushrooms are in world 2 boss castle(to unlock world4) and world 5 boss castle(to unlock world 7) you have to beat the worlds 2 &7 boss when your mini Mario, in order to unlock worlds 4 & 7, it will be a little difficult beating the bosses when your mini Mario but it's worth it