The Sierra-helmed one
So this isn’t the kind of revival you see every day.
Rewind back to 1997: a year after the original Diablo launched on PC. Sierra actually developed an expansion for it called Hellfire, which added several new components in (most notably the Monk class, on top of the existing Warrior, Rogue, and Sorcerer) as a sort of side story.
It failed to take off and was labeled as “non-canonical,” and was very quickly forgotten and went out of sale rotation. To this day Blizzard very rarely, if ever, even acknowledged that it happened (no references to Hellfire are present in the Diablo III anniversary event). Yet, GOG is now offering the expansion as part of their original Diablo package, where it’s included in the $9.99 (currently $8.99) sale price as a sideload option.
I actually remember picking up Hellfire back in 1997 and thinking it was fine. It sure felt like a non-official expansion (and given how hefty PC expansions were back then, it really felt more like a DLC, even though the term wasn’t used at the time), but the Monk class was enough of a reason to warrant another playthrough, as were the new enemy types, extra dungeon, and small quality of life upgrades.
I’m sure Blizzard sees it as a weird chapter in their life, before Diablo II absolutely exploded, but it’s worth revisiting.
Diablo + Hellfire [GOG]