The crew filmed a number of shots on video as reference material for the CG animation in the game's cinematics. While filming, elements such as dust were shot, which were never intended to appear in the final product. However, the staff felt that it gave a good effect, and so it was later added to the CG animations.
It was originally intended for the game's cinematics to explain why Marius is found within the room in the opening and closing cinematics, but it was omitted. The building was intended to be a sort of asylum, as he had gone crazy after everything he had seen, and that he was found screaming about the events that occurred before he was taken in.
Act IV's cinematic was the final cinematic to be completed during development, as there was a lot of debate as to which demons would appear.
The hellgate shown during Act IV's opening cinematic contains the faces of various members of the ##Blizzard## staff.
The only non-CG element within all of the game's cinematics is the liquid in the back of the cinematic openings. These were used from photos taken of moving liquid, originally used in the original Warcraft trailer.
The tavern shown during the game's prologue was originally conceived as an opium den, but it was changed in order to tone down the setting.
During the game's prologue cinematic, a clip of skeletons tormenting Marius' mind in front of a flaming backdrop was included as a tribute to the 1963 film, Jason and the Argonauts.
The developers went with flashback style sequences for the game's cutscenes so that they could make it from the perspective of a third person, as making the playable characters appear within the cutscenes was beyond Blizzard's capability at the time. They were designed to not only follow along with the game's story, but to show players the other side of the story that wasn't within the game.
The Secret Cow Level was created after rumors spread online of a "Secret Cow Level" being available in the original Diablo. Of course, these rumors were false, but it is believed that the inclusion of such a level in Diablo II was to appeal to fans of the series. Blizzard has since made many references to the phrase "there is no Cow level" in their other games.