The Harvester (http://darksiders.wikia.com/wiki/The_Harvester) was a preorder bonus on the XBox 360 and PS3 versions of Darksiders 1. Thought to be inaccessible in all PC versions (including the Hellbook Special Edition), I've found a save file hack that unlocks it.

NOTE: Numbers beginning with 0x are in hexadecimal format.

NOTE2: Make backups of all your saves before doing this. I'm not responsible for loss of saves!

NOTE3: Please help me test this hack more thoroughly and provide feedback here. In particular, testing is needed to confirm whether or not The Harvester drains more souls as opposed to the default Scythe and also whether or not all abilities can be purchased and used correctly. If anyone also has the PS3 or XBox 360 version of the game, I would greatly appreciate it if you could do a side by side comparison of the weapon between the versions.

What's needed:
- offzip (http://aluigi.altervista.org/mytoolz/offzip.zip)
- packzip (http://aluigi.altervista.org/mytoolz/packzip.zip)
- a hex editor (I use HxD)
- a Darksiders save file just after meeting Vulgrim (other save locations might work as long as the Scythe has not yet been purchased)

Steps:
1) Place offzip.exe, packzip.exe, and the save file (referred to as dssave0.dsav below) in a folder
2) Open a command prompt in that folder
3) Create a temp folder with the following command: md temp
4) Extract dssave0.dsav with the following command: offzip -a dssave0.dsav temp 0
5) Open temp\00000039.dat in your hex editor
6) Search for the text string hellraiser/hellraiser
7) Change the 01 0x3D bytes past that string (at offset 0x732B for me) to 00 (see disable_scythe.png)
8) Search for the text string harvester/harvester
9) Change the 00 0x3D bytes past that string (at offset 0x739B for me) to 01 (see enable_harvester.png)
10) Save temp\00000039.dat in the hex editor
11) Recompress dssave0.dsav with the following command: packzip -o 0x00000039 temp\00000039.dat dssave0.dsav
12) Copy dssave0.dsav into the Darksiders saves folder

Explanation:
In step 7 we are disabling the default Scythe (apparently called "hellraiser" in the game's code) in Vulgrim's shop. In step 9 we are enabling The Harvester in the shop. I don't know yet whether The Harvester drains more souls than the default Scythe. I also haven't figured out how to make The Harvester free like in the console versions.

Credits:
Save file editing instructions were adapted from this post.

Pre-hacked save files available for testing:
- Beginning of game (Harvester available when you meet Vulgrim)
- After collecting souls for Vulgrim (~500 souls + 1 artifact)
- After collecting souls for Vulgrim (50,000 souls + lvl1 Harvester)
- After collecting souls from Vulgrim (50,000 souls + lvl5 Harvester)

WoW! Now that's something.

If anyone has the XBox 360 version, I would really appreciate it if you could post 2 links to save files: both right after receiving the Horn from Vulgrim but without buying anything, the first without unlocking the Harvester (default Scythe in store) and the second just after entering "The Hollow Lord" in the options menu. In addition, a third save file just after buying the Scythe and a fourth just after buying the Harvester might also be helpful for comparison.

PC version here, and your instructions worked really well. Thanks also for the links and names to the programs used. Harvester looks wicked cool. :)

Glad you find it useful! Are you using the GOG or Steam version of the game?

GoG. Steam hasn't had a sale on these for a bit, then GoG did one about new DRM shackles broken sale. No achievements, but that's okay. Your fix is still working fine and dandy. Love the look of that harvester as it reaps spider souls while grinding.

Steam had a midweek madness sale on the Darksider franchise, so picked up the package for 12USD. Followed instructions once a save was made in Crossroads, and confirmed that Harvester was available by Vulgrim with a Steam save. Instructions for windowed mode also work just fine.

As to your earlier query regarding Harvester bonuses and suchlike, I really can't say. All I can say is that I do love the styling of that scythe skin. :)

Thanks for the report faxfane! I've mentioned you in the thanks portion of my guide in the Steam discussions here.

Check the two screenshots attached at the bottom of the original post. The digits in red are the changes made in steps 7 and 9.

Thank you! I really, really wanted to get a hold of this item...

Now, if only a save file hack existed for 2, to import "Pauldron of the Horseman", "Chaos Fang Scythes" and "Crow Armor Set"...

Those items are likely still in the game's code, much like the Harvester in Darksiders PC. I would be more than happy to analyze XB360 save files for Darksiders 2. For each item, I would need a save file just before obtaining it and just after obtaining it. The saves should be as similar as possible (same location, same point in the story line, etc.) so that I can more easily analyze the differences made to the files upon receiving each item. I could also use 4 XB360 saves from Darksiders 1 as well (outlined here).

Guys its works! But you have to edit save file named: dsauto.dsav

All is ok but in step 4. type command: offzip -a dsauto.dsav temp 0 and in step 11 type: packzip -o 0x00000039 temp\00000039.dat dsauto.dsav.

The Harvester is so awesome! :)

Good luck guys and thank you @bryanburke :)

Do you, by chance, also know how to edit the location? I.e. which map one is on? I have encountered a game breaking bug: For some reason the Twilight Cathedral shows up as 'Unexplored' on my Serpent Holes map. So I can't travel there and can't finish the game, since the serpent holes are the only way of going back to the Twilight Cathedral. So it woul be very nice to have a savegame manipulation to 'teleport' there. Or a way to edit which locations show up as explored would be helpful too.

Unfortunately, I don't have any knowledge on location editing. I know there's a save editor floating around online somewhere, but I've never used it.