Download GZDoom and extract it into your game directory (often C:\GOG Games\Heretic Shadow of the Serpent Riders\base ).
Unlike Doom , Heretic lets you carry items to use whenever you want. This is key to surviving the harder, later episodes. Heretic.Shadow.of.the.Serpent.Riders-GOG.rar
Supercharges your weapons for 40 seconds. For example, the Hellstaff will rain fire from the sky, and the Phoenix Rod becomes a flamethrower. Download GZDoom and extract it into your game
This "Shadow of the Serpent Riders" edition includes the original three episodes plus two additional high-difficulty campaigns: Supercharges your weapons for 40 seconds
The most "useful piece" for this specific GOG release is to use a modern source port like . It updates the game to support high resolutions, widescreen, and modern control schemes (like vertical mouselook). How to set it up: Install the game from your GOG library .
Run gzdoom.exe . It should automatically detect the HERETIC.WAD file and launch the game with modern features.