Dungeons & DragonsDiablo II was adapted into a set of two D&D rulebooks: Diablo II: Diablerie, published in 2000, and Diablo II: To Hell and Back, published in 2001, in addition to which a Diablo II set for the Dungeons & Dragons boardgame was released by Wizards of the Coast in 2000.
PromotionBlizzard itself produced an action figure line, with figures depicting the Barbarian, the Unraveler, and of course, Diablo. They also released a whole stack of merchandise, including Zippo lighters, wristwatches and mouse pads, all in limited edition.
References: DiabloThe much rumored and non-existent secret "Cow Level" from the original game was actually added to Diablo II. It is just a flat plain, populated by bipedal cows, which go "Moo! Moo!" in deadpan human voices. The level also features a boss, "The Cow King", who looks just like all the other cows.
In Act I, the player can enter a portal to the town of Tristram, now destroyed by demons. Some characters from Diablo can be seen there. Decard Cain and Griswold the Blacksmith are alive; the former will help the player with his quests while the latter is possessed by evil powers. The remains of Wirt the Peg-Legged Boy can also be spotted; his leg allows the player to enter the cow level.
ReferencesOnce in a great while, one of the zombies can be heard uttering "brainsss". This is a reference to the numerous Living Dead movies, in which zombies hunger for human brains.