AY YO, STOP NOW, AND LEMME REDIRECT YOU HERE:
http://www.gamefaqs.com/boards/762804-monster-hunter-4-ultimate/72570518THE STUFF BELOW IS OUTDATED AND MADE BACK WHEN EVERYTHING WAS NEW AND SHIT. IT'S WAY BEYOND THAT NOW. IF YOU STUMBLE ACROSS THIS SOMEHOW THE RESOURCE ABOVE IS INFINITELY MORE USEFUL.
OK THANKS.
A image-based guide on how to start creating your own custom DLC quests.
Svan - Creator of tools to encrypt/decrypt files
Kyo_100 of GameFAQs for original guide
APM - Creator of the simple dlc edit tool
v1.0 - FINAL
Wow, APM has made it so that you literally don't have to do anything except upload. I updated the sections accordingly. TBH this guide is now obsolete LOL. Will keep it for sentimental reasons Kappa
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v0.4
Updated links
Cleaned up/reworded some sections for easier comprehension (hopefully)
Added a brief FAQ section
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v0.3
Added APM's complete DLC edit tool
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v0.2
Added APM's supply box dlc edit tool
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v0.1 - Original guide write-up
Necessary files:
Easy (recommended)
SKFU Proxy
APM Full DLC Editor Beta
All decrypted DLC quests
Puu.sh1. Download all the files...
2. Unzip them...
3. Open them up with the DLC editor
4. Edit whatever fields you want, check FAQ section for more details.
5. Save as ENCRYPTED once you're done.

6. Follow this guide to use it on your N3DS, ignore all the encryption parts:
GUIDE by TeamFortifier7. Alternatively start at step 4b. below.
AND THAT'S ALL FOLKS.
Advanced (not recommended)
svanheulen's mhef files to encrypt/decrypt ("Download as Zip")
Python 2.7
PyCrypto
SKFU Proxy
Item Database (data.db)
SQLite Viewer - Portable app recommended
Hex Workshop
APM Full DLC Editor Beta
All decrypted DLC quests
Puu.sh1. Installing Python and PyCrypto1a. Run the Python 2.7 installer.
1b. Open up a command prompt (Start->type in cmd->Enter) and type in python - if it works, you will see a dialogue. Type exit() to quit.

If you get this:

Open Start -> Control Panel -> System -> Advanced System Settings -> Environment Variables
Under System Variables, you'll see a Variable called PATH or Path, double click the 'Value' portion, and add ;C:\Python27
So if it was
C:\System32\
It will now be:
C:\System32;C:\Python27

1c. Install the PyCrypto package for Python 2.7. If you have trouble with this part, disable any anti-virus temporarily and try again. They might be detecting it as malicious.
2. Unzipping the rest2a. Unzip the mhef files, if should be called mhef-master.
2b. Open a command line in mhef-master (You can shift+right click and select "Open Command Prompt in this Folder")

2c. Copy+paste or type in the following command:
python setup.py install
You should see something like this afterwards:

2d. Set up your puu.sh account.
2e. Unzip the decrypted files.
2f. Unzip SKFU proxy.
3. Using APM's DLC editor toolThis part is fairly straight-forward, open up the tool, you'll see something like this.

For the purpose of this guide, we'll use m60239.mib - Protector of Peace, a G1 quest - Kill a Tetsucabra and a Frenzied Tetsucabra
3a. Make a back-up of the decrypted .mib we want to edit. Create a copy, then rename it to m60239_d.mib or something like that.
3b. Click load, and select the m60239_d.mib file to edit.

3c. Change anything as you see fit! Refer to FAQ for description of fields.
4. Encrypting the file and downloading it onto your 3DS. 4a. To encrypt this file into something usable on the 3DS, move the edited file into a new folder, open a command terminal in that folder by and use this command:
python dlc.py e USA m60239_d.mib m60239.mib
This will create a new m60239.mib that you can now download onto your 3DS. If you're in another region, use EUR, JPN, or KOR.
4b. We want to upload this file to puu.sh for use. Open up the puu.sh window:

Change it so that you upload a file when you double-click (my preference), but you can just upload via right click. Upload your m60239.mib file.
Puu.sh will automatically copy the link once you do.
4c. Now make a file using Notepad called rules.httprls and put this in there:
http://goshawk.capcom.co.jp/3ds/mh4g_eu_/m60239.mib
http://puu.sh/iQVUX/c120b9257f.mib << your puu.sh link that was copied
http://goshawk.capcom.co.jp/3ds/mh4g_us_/m60239.mib
http://puu.sh/iQVUX/c120b9257f.mib << your puu.sh link that was copied
An example of a file with many DLC will look like this:

Make sure you save it as 'all' and not as a .txt

4d. Run SKFUpr0xy.exe

Import rules into HTTP(s). It should detect automatically your proxy IP. Setup your 3DS to connect through this proxy, there's plenty of guides on that already. Press Start.
4e. Go on MH4U and download the quest, it will be called Protector of Peace. If you already have it, check it again and redownload + save.
4f. Go to a G-Rank hall, go to event quests, and run it. You should be playing your edited quest instead.
Downloading your first DLC quest from Capcom serversFor this example, we'll be using the DLC quest Protector of Peace as our initial subject. It is a G1 rank quest - Kill a Tetsucabra and a Frenzied Tetsucabra
1. Open a command line in mhef-master\tools.
2. Enter this command:
python download_n3ds.py USA m60239.mib m60239.mib
You'll now see a m60239.mib file in your folder. All region codes: USA, EUR, JPN, KOR.
3. Copy this file to the mhef-master\examples\n3ds folder, open another command line here.
4. To decrypt this file into something editable, use this command:
python dlc.py d USA m60239.mib m60239_d.mib
5. Now, open up SQLite browser, and open up Data.db. Go to Browse Data and select the items table.

To find a specific ID of an item, type the EXACT name into the filter. Use Kiranico if you don't know the exact name.
6. Open up the m60239_d.mib with Hex Workshop, you'll see something like this:

So for now, we'll cover how to edit supply box.
Start a search for Hex Values (CTRL + F)

We know from playing the game that this quest's initial supply box has 15 Freeze S.
The item ID in DEC(imal) for Freeze S is 105. We need to convert this to HEX in order to edit our quest.
To do this, use a
Dec to Hex webpage, or a notepad++ plugin that converts this stuff automatically.
We see that 105 becomes 69.
These supply box values are in 4 bytes, which means if it ends up being something like 69 we'll add a 0 in front of it. So it becomes 00 69.
However, the way these bytes are in the file are reversed per 2 bytes, so it actually becomes
69 00.
Now, in the supply box there's 15 of these, we convert 15 to hex, to get F. This is also in 4 bytes, so it would be 00 0F. Similarly, inverting this gives us
0F 00.
So if we put this all together, we'll get
69000F00
Searching for this string will bring us to a specific location.
Now, let's say we want to replace this reward with something like a Fatalis Flameshell.
Fatalis Flameshell ID: 1590
->HEX-> 0636 ->INVERSE-> 36 06
So to edit, just click in front of 69 00 and replace with 36 06.

If you want to change that 15 to 99, convert 99 to hex -> 00 63
Invert, 63 00. Replace 0F 00 with 63 00.
You just edited your supply box from 15 Freeze S to 99 Fatalis Flameshells!
I have a 32-bit system, and I can't use the installer for the 64-bit system.It is for x64 bit systems, if you have a x86 (32-bit) system, install the following:
Python 2.7 for 32-bitand
PyCrypto for 32-bitWhat are the IDs of quests, monsters, and items?
Quest IDs.
Monster IDs
Item IDsCourtesy of APM
What do all those fields in APM's tool stand for?Quest InfoQuest ID: The ID of the DLC quest according to
this list.
Carve Table: Number of carve tables
Stars: Difficulty
Sub HR: HR deducted on failure
Penalty: HR Points deducted on failure
Sub Cash: Zenny deducted on failure
HR Points: HR points awarded on completion
Fee: Initial zenny paid to start quest
Cash: Zenny awarded on completion
Time: Time limit
Terms 1: Condition that must be fulfilled prior to completing quest
Terms 2: Condition that must be fulfilled prior to completing quest
Quest ObjectivesThese determine the type of quest (collection, hunting, etc) I wouldn't worry about them too much.
Boss tabBoss monsters that will appear.
MonstersRegular monsters that will appear. Go felynes!
Supply BoxEdit the initial supply box here. Double-click then type for a quick search.
RewardsEdits the 3 reward boxes. Note that % must add up to 100 or else you can't accept the quest later on in game.