On the 31st of December, it would have been 20 years since the original Diablo was released to the world. To celebrate this momentous occasion, Blizzard will be rolling out a bunch of Diablo-themed content across all of its games.
For Diablo III, Blizzard will be sending players on a nostalgic trip as an update for the game will bring with it the Darkening of Tristam event. This event is essentially a ‘reimagined’ version of the Diablo’s first level in the Diablo III engine.
Outside of Diablo, Blizzard’s Diablo celebration will come in the form of cosmetics. For Heroes of the Storm and Starcraft II, the games will be receiving Diablo-themed portaits, the former for your profile while the latter for your workers. Hearthstone players will see a hooded stranger in the Tavern Brawl mode that carries a ‘grim deck’ with him. World of Warcraft players will see characters from Sanctuary appear in Azeroth. Finally, Overwatch players will be getting in-game sprays and player icons modeled after Diablo himself.
Source: Battle.net