I'm surprised that NOBODY over the years has ever made a save editor for this game. Well, now there is! NSMBDS SE can edit all 3 files in the game with the following options:

Life Count
Coin Count
Star Coins
Score
Mario/Luigi's current powerup
Inventory item
Bottom Screen BG

It can also unlock all the worlds in the game, as well as all the levels. (Be warned, as unlocking all the levels without unlocking the worlds first results in some small weird things that occur on the worldmap!)

How to use? Dump a .SAV file. (currently no support for other save types) To get your .SAV savefile, you can choose 'Export Backup Memory' in DeSmuME, use TWLTool on your 3DS with homebrew, or however else you wish/know how to retrieve a .SAV save from NSMBDS.

Screenshots:


You can download v1.0 right here:
https://github.com/newluigidev/New-Super-Mario-Bros-Save-Editor/releases/download/v1.0/NSMBDS-SE-V1.0.zip

Oh and, thanks to these awesome people for their help!
 RoadrunnerWMC: Checksum RE & Python script, code help
shibboleet: Savefile documentation

The program is great, but the star coin number doesn't seem to be working.
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Check out these awesome hacks! Beyond DS is now my major hack!

Yeah, I had issues with that too. I'm not sure why it does that, I'll look into it.

i think you should add a level select in wich you select wich starcoins you have in a ceretain level, but that would probably be a lot of work

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anyways, keep doin' what youre doing

Yes, you're right about that.

It actually shouldn't be that much work.

It's not like NLD has to do it seperatly for each save/level like he did the existing stuff
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GitHub - Kuribo64 - YouTube

Wow, nice work!

Oh boy this is what we didn't knew we needed but now we need
Good job?

Hey I have an issue. When I edit my sav file, and load the file in-game, I get a black screen. Anyone else get this issue? I'm using the 3Years of NSMBHD rom I made from the 3Years patch I downloaded from here.

The link won't load. Could you use MediaFire or something?
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One small step for man, and a flag too, I guess.

It works for me.
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Nothing to say, so jadnjkfmnjamnfjkldnajfnjkanfjdksan jsdnvj m.

Hello again community, I just download the nsmbds save editor onto my computer so I can unlock all the exits/worlds. I followed all the procedures and loaded the .sav file into the editor. I unlocked all the exits/worlds on the editor and put the file back into the micro sd(I'm using an r4). Whenever I load the file on the game that I'm playing, I get a black screen and the game freezes. I don't think I'm doing anything wrong but if I am, can someone plz help. Thx.

Wa it's good! I will test it now! For the new ones that are developing it's good so we don't have to do all levels again and again