The mask Michael wears is the exact same mask (a repainted and modified Captain Kirk mask) worn in the original Halloween (1978) film. It looks different in the sequel because the paint had faded due to a few reasons, first because Nick Castle, the original Michael, kept it in his back pocket during shoots. Also, Debra Hill kept the mask under her bed for several years until the filming of Halloween II, causing it to collect dust and yellow because Hill was a heavy smoker. Also, the mask appears wider because Dick Warlock is shorter and stockier than Nick Castle, so the mask fit his head differently. As the producers thought it would be the final sequel in the series, they let Warlock keep the mask, scalpel, boots, jumpsuit, and knife used in filming. When they decided to revive Michael in Halloween 4: El regreso de Michael Myers (1988), the producers realized they had made a mistake and never again gave props out to the cast and crew, therefore subsequent sequels used different masks that looked rather different.
(at around 11 mins) The voice of Alice's friend (heard over a telephone) is the voice of Nancy Loomis, who played Annie in Halloween (1978), and appears in "Halloween II" as the corpse of Annie.
To get the role of Michael Myers, Dick Warlock revealed that as he passed by a room, the Michael Myers mask was on a table. He put the mask on and walked into Rick Rosenthal's office and stood there. After Rosenthal continuously asked him who he was and he didn't reply, he took off the mask and asked if he could play Michael Myers.
The film is set immediately after the first Halloween (1978). Since Jamie Lee Curtis had begun to wear a much shorter hairstyle in the 1980s, she had to wear a wig that matched her original hairstyle for the film.
Producer/writer John Carpenter didn't like director Rick Rosenthal's first version of the film, believing it to be as scary as an episode of Quincy M.E. (1976). A re-edit was done, but Carpenter still found it too tame, so he took over the editing process and sped up the action. He also shot a few gory scenes that were added into the film despite Rosenthal's objections. This annoyed Rosenthal because he had wanted the sequel to emulate the way the original avoided explicit violence and gore in favor of well-crafted suspense and terror. In fact, Carpenter had intended for "Halloween II" to do just that, but the success of the new wave of slasher films in 1979 and 1980 made him afraid that a film which was scary and R-rated but lacked bloodshed and nudity would do poorly at the box office, leading to the extra graphic material inclusions. He later said that he thought that Rosenthal didn't have a "feeling for what was going on" with the film." Rosenthal would go on to direct Halloween: Resurrección (2002).