If you are attempting to run the original Diablo or source ports (such as DevilutionX), the game executable requires diabdat.mpq to be present in the installation folder. Without this file, the game cannot load assets and will fail to launch.
While some logic is hardcoded in the .exe , the MPQ holds the data for randomly generated dungeons and item properties. Diablo 1 Diabdat.mpq
You lean back. The screen glows in the dark room. The archive is still open. All the dead bytes, the compressed dreams, the terror and the triumph of a small town called Tristram, sitting in a single, unassuming file. If you are attempting to run the original
Interestingly, some versions of the MPQ even contain an embedded debug release of the original game's executable, which proved vital for modern reverse-engineering efforts. Where to Find the File You lean back