Getting Started

This guide will get you up and running with the necessary tools for modding NSMB2.
Let me know if you have any questions, or feel free to ping me for help in NSMB2 Hax's #nsmb2-help channel!

You can grab a copy of the game for your PC by dumping a legit version of the game from a homebrewed 3DS.
I can't help you get the game otherwise!

3DS Homebrew Guide · Dumping Titles and Game Cartridges

You'll need the following:

• New Super Mario Bros. 2 ROM
• Windows/macOS/Linux PC

Dumping the ROM Files

1. Download Citra, the 3DS emulator.
2. Place your ROM file in a directory that's easy to find, such as Documents/My Games/ROMs
3. Open Citra and double click on + Add New Game Directory. Choose the folder where you placed your ROM.
4. NSMB2 should now be listed! Right click on the game and click Dump RomFS. A folder will open where the game files were dumped.
5. Go up one folder, and copy the 0004000XXXXXXXX folder to a directory somewhere safe, such as Documents/Modding/.

Nice work; you have just extracted the game files from the ROM! We'll need these to make edits to the game.

Setting Up CoinKiller

CoinKiller is NSMB2's level editor. You can use it to make edits to both levels and tilesets.

Now for a bit of context: NSMB2 mods work by layering modded content on top of an existing ROM file's contents. This is called LayeredFS.
Both Citra and Luma3DS support these types of mods out of the box!

This means that you only need to distribute files you've changed in your mod to play it on other systems. For example, if you only edited the first level (1-1.sarc) in your mod, then you would only need to add that specific file to your mod, which will be layered on top of the rest of the base game.

First, let's set up CoinKiller, the level editor for NSMB2:

1. Download CoinKiller, then extract the .zip file (if you're on Windows) and place that somewhere safe.
2. Go into Citra, right click on NSMB2, and click Open Mods Location. This is where Citra loads the mod, and also where you will develop and test your mod!
3. Navigate to the romfs folder. (I will now be calling this folder the mod folder.)
4. Find the dumped game files which you previously extracted, and copy the Unit folder into the mod folder.
5. Create a folder called Course in the mod folder, and copy Course/1-1.sarc into it from the game files. (Or copy all of the levels, if you wish to look through them or edit them.)
6. Open CoinKiller. Go to File > Load unpacked RomFS… and choose the mod folder.
7. You should now see 1-1 in CoinKiller!

You can add more in-game levels either by dragging them in from your dumped game files.
You can also add a blank level by clicking Add Level from within CoinKiller.

Editing and Testing

Let's add a modification to 1-1 that makes the level a bit harder. We'll do this by setting a time limit for the level, changing the level's aesthetics, and adding some poison!
Don't forget to make backups of your own work!

1. Double click on World 1-1 from within CoinKiller.
2. You'll see the level, and a toolbox on the right side with several different options:
   
   1. Area Settings contains values for the area, such as the time limit.
   2. Tileset Palette contains tiles from four different categories: Standard, Stage, Background and Interactive.
   3. Sprites contains an ordered list of sprites, such as enemies, red coins, special blocks, platforms, and event controllers.
   4. Entrances contains your area's entrances between other areas. This includes subworld transitions.
   5. Zones has a list of your area's zones, which are like different sections of your level. An area can have multiple zones in it.
   6. Locations has a list of your area's locations, which are generally used for events and scripting reasons.
   7. Paths contains paths which certain sprites need to navigate on.
   8. Progress Paths contains your area's progress paths, which are used to display the bottom screen progress UI.
      
      • Every area needs a progress path to not crash! Make sure to place it from your level entrance to the end of the section at the exit, or at the base of the flagpole.
3. Click on the Area Settings tab (the gear) and set the Time Limit to 200.
4. Click on the Sprites tab (the goomba). Search “Poison” and place it at the very bottom of the zone, so you can barely see it.
5. How about a change of aesthetics? Click on the Zones tab (the blue square) and click Zone 0. Change the music to Mushrooms/Athletic. Then click Open Background Editor and choose SMW Mountains.
6. Save the level with Ctrl+S (Cmd+S on macOS).
7. Open Citra and launch the game!
8. Enter the first level in a new save file. You'll now see your changes!

Remember to playtest your level when you make changes! Try to be particular about your design choices, to make the level as fun as possible. It may help to search up Mario Maker level design tutorials on YouTube for inspiration!

Resources

• NSMB2 Hax Discord Server: Ask questions and browse through mods here!
• NSMBHD's NSMB2 Wiki: Contains lists for every asset in the game, including file formats, models, tiles and layouts.