Pond86: So Hellfire from CD works fine with GOG's version. Heres how to do it. I did this under Windows 10.

For original Diablo (Non GOG scroll down.)

1) Install Diablo. (GOG's install should run fine.)

2) Install Hellfire. (HD Voices are optional.)

Make sure to not let Hellfire update via setup or register or anything.

(Setup should run if it fails to then copy the following files from the Hellfire CD to a new folder in your Diablo folder.) (Feel free to name the new folder to whatever you want.)

You will need:

hellfire.exe
hellfire.mpq
HELLFRUI.DLL
hfmonk.mpq
hfmusic.mpq
hfvoice.mpq
storm.dll

(If you have copied these files across rather than running setup.exe then skip to step 4.)

3) Go to C:\SIERRA\ and copy the entire HELLFIRE folder to your Diablo installation.

4) Download Hellfire Enchanced If you don't do this then Hellfire will ask for the Diablo CD. It shouldn't change anything else other than making Hellfire more reliable under newer systems. Extract it to Hellfire's folder and replace anything it wants to.

The game should then run from hellfire.exe.

You can then uninstall Hellfire and Sierra Utilities from Settings then Apps if on Windows 10 or Control Panel on others or 10, as uninstalling it through Sierra Utilities does nothing. If you just copied the files over then you can ignore this.

[Optional] To get Hellfire running using GOG's wrapper (as discovered by Realpsojed):

1) Run Diablo Launcher from GOG, select Video Settings and setup your graphics.

Recommended setup is:
Display mode: Same as Desktop
Presentation: Windowed - integer scaling

2) Copy the ddraw.dll, dxcfg.exe and dxcfg.ini files from Diablo\dx into your Hellfire folder (replacing the files it wants to replace.)

Next time you run hellfire.exe it should work at a higher resolution though much like GOG's version you will get black bars down the side of widescreens.

Any issues with the above feel free to ask here or PM me and i'll try to help you.

Loonwed: Will be there extansion Helfire on GOG to buy?

dudalb: As of June 5, 2019 you don't even have to buy it. Hellfire is now on GOG as a free bonus DLC.

lumin: UDP is not working for multiplayer in Hellfire. Here is how you get multiplayer working.

1. Download IPXWrapper
2. Open the archive and extract the following 4 DLLs into your Hellfire folder.
dpwsockx.dll
ipxwrapper.dll
mswsock.dll
wsock32.dll
3. Run the game with Hamachi (or your favorite VPN) and choose the IPX option.

Works flawlessly for me.

Mephtoline: Uhhh, computer illiterate here, can't find a Hellfire folder. Gog says I di.

mehmetozen: I am grateful to you. Hellfire, you said no. I wanted to buy it. I have my old laptop, but I wanted to play from my own main PC.

THANK YOUUUUUU :) =) :D

Jerjew: As someone new to all this (only played Diablo 1 on Playstation when I was a kid) I'm finding all of these posts very confusing. I only have the GoG version that comes with the Hellfire expansion. Unfortunately, the expansion doesn't have a multiplayer option at all. Is there a simple thing I can download to add the multiplayer option to play with 3 friends as vanilla as possible and with the updated resolutions? It'd be fun to for us each to be a different class.