Since you have been asking for it, I have been trying to create a patch for the Deadlock 1 GOG version that allows multiplayer games.
This is my best result so far, unfortunately it's lacking background sound and music, I still do not know how to solve it without resulting on a very unstable version (that crashes before someone is able to play).
I have created it about two months ago, I was only considering posting it after I fixed the sound issue, but I couldn't yet, then I posted it as is. The audio from videos work. [EDIT] Compatibility mode can fix the sound issue. See updates below.
The patch file is attached, you need BSPATCH to apply it to DEADLOCK.EXE.
How to apply:
Get yourself bspatch (usually comes with bsdiff).
Windows version links:
https://www.pokorra.de/coding/bsdiff.html (Compiled with GCC 3, for old Windows 32-bit versions)
https://github.com/cnSchwarzer/bsdiff-win/ (Compiled with VC 2015, requires recent Windows versions)
http://sites.inka.de/tesla/download/bsdiff4.3-win32.zip (Old link)
Run bspatch using cmd or other console/terminal tool like this:
Code: Select all
bspatch deadlock.exe deadlockpatched.exe deadlockmppatchfor20011.zip
Then run deadlockpatched.exe when you want to play with MP enabled. Please post here if it works.
It should work with other computers running the same patched version and with Deadlock 1.31 (CD version with update).
GOG disabled multiplayer because it cannot be run on Windows Vista or 7, the latest windows that should run it natively is Windows XP 32 bit. I have tested it on Windows XP 32 bit and Windows 2000 successfully.
It might work on other windows when using modem or serial connections.
[UPDATES for Newer Windows]
Crashing on "newer-than-XP/7" Win64 Versions:
MildewMan1's "HOW TO: Fix issues with crashing and freezing"
 Added new links for bsdiff for Windows.
I have asked them if they would help me on this patch or release a non-supported version and they said it's against their rules. Still I thank their time for answering me.