Blizzard announced at Blizzcon 2016 that the Darkening of Tristram update for Diablo III would be a remake of the original Diablo in celebration of its 20th anniversary. During the Diablo 20th Anniversary Panel, Blizzard revealed that the Darkening of Tristram would be a yearly event occuring every January.

Gaming news sites Gameranx and GameRevolution and tech news site Motherboard reported that Blizzard announced at the close of the opening ceremony of Blizzcon 2016 that the upcoming free content update for Diablo III, Darkening of Tristram, would be a nostalgic celebration of the 20th Anniversary of Diablo by recreating the events of the original Diablo. According to business magazine Forbes and gaming sites VG247 and Polygon, the Darkening of Tristram would be a limited-time annual event taking place during the month of January, paying homage to the original game. Blizzard explained that, although the original Diablo was released on December 31, 1996, most players were only able to play it the next month, January, the following year.

To access the remade classic Diablo levels in Diablo III, with the content update, players need to travel to Old Tristram in Adventure Mode where they will find a portal that will take them to a recreation of events from the original. Players will enter the Cathedral in the town of Tristram where they will delve below the town, down through 16 dungeon levels, where they will find events, monsters, classic enemies, all 16 levels, recreated as they were in the original. They will encounter all four bosses from the original game, namely, the Butcher, Skeleton King, Lazarus, and finally, Diablo himself.

The remake tries to capture the look and feel of the classic game. A pixelated graphic filter is applied to the game which Frank Pearce, the chief development officer of Blizzard, calls "glorious retrovision." The music is from the original game, which was composed by Matt Uelman. The audio is "tinny on purpose." The frame rates are 25 percent less to give the game a slight stutter. The controls are restricted to the classic 8-directional movements. The remake also has a retro user interface.