He ran the patch. A DOS prompt blinked. Patching DIABLO.EXE… Sector rewrite complete. The Soulstone is broken.
The most straightforward "patch" is simply using the GOG.com version of Diablo. diablo 1 no cd patch
For most retro enthusiasts, this is the gold standard. It isn’t just a No-CD patch; it is a complete engine overhaul that acts as a wrapper for the original game. He ran the patch