PATCHING INSTRUCTIONS:

In order to play this hack, the first thing you're going to need is a clean (U) region ROM of New Super Mario Bros., due to legal reasons, I'm not allowed to distribute one and I can't tell you where to find one, but your dear friend Google may be able to help, you can also legally obtain your own copy of the game.

Step 1: Open "xdeltaUI" and go to "Apply Patch".

Step 2: In "Patch" click "Open" and select "SMB. The Missing Lands DEMO v1.2.xdelta".

Step 3: In "Source File" click "Open" and select your clean (U) New Super Mario Bros. ROM.

Step 4: In "Output File" click on the three dots and select the place where you want to save the hack in your desktop (Preferably in a place you can remember :P), type the name of the hack followed by the ".nds" extension and click "Save" and then click on "Patch", and then you're done, now you're ready to play the hack :D.

Step 5: Enjoy!!!

ADDITIONAL: If you're on a mobile device and you can't use xdelta, you can try an app called UniPatcher.


KNOWN ISSUES:
"I can't patch the game, when I click on Patch, it gives me an * Xdelta3: target window checksum mismatch: XD3_INVALID_INPUT* error"
- Make sure the NSMB rom you're patching is (U) region and not (EU), also, make sure the rom you're patching is a CLEAN ROM (By clean ROM I mean a ROM hasn't been opened in any editor or external program).

"I followed every step carefully and I'm using an (U) rom and I'm still getting errors"
- If xdelta doesn't work for you, you can alternatively use this online patcher (https://www.hack64.net/tools/patcher.php), it's almost similar to xdelta and skips checksums.

If you tried both options and you still can't patch the rom, then try getting another NSMB rom, and if you're still getting errors, then I'm gonna throw the towel and cry like a baby all day :P.