This only works with Duke 3D v1.3 (ie a non-atomic version of duke3d.grp). This is a total conversion, having completely brand new textures and unique environments, from dark dingy castles, to dark forests. All new weapons. Its also one of the hardest mods available, so only veteran Duke3d players are recommended to play it.
This guide is for win7 64 bit OS using eduke32, written November 1,2017.
Mod is for original version of game. (as author said DO NOT use atomic version of duke3d.grp)
1. Create a txt document in the folder you unzipped this mod to.
2. add this line>>>>> eduke32.exe /ggrune.grp /xgrgame.con <<<<<<<<<< no arrows and save the txt document.
3.Rename txt document to anything you want (i used Gamestart) so my file shows up as Gamestart.txt
4.(THE MOST IMPORTANT STEP)Rename Gamestart.txt to Gamestart.bat you need to disable hidden file extensions in windows to do this.
5. (FINAL STEP) unzip eduke32 program to the same folder the mod is in and throw your copy of duke3d.grp in there aswell. Now just double click the Gamestart.bat and click start in eduke32 when it opens you should see Grune in the episodes list.
EDIT: I Installed the patch for this mod by changing name of new.grp to Drune.grp and replacing the old Drune.grp. And the game/mod seems to be working fine still.(not sure if its working the way its supposed to though I've not fully played it through yet)
I recommend playing without patch first before trying with the patch just incase, but its up to you.