Jamie Lee Curtis, Charles Cyphers, Kyle Richards, Nancy Stephens, and Nick Castle were in the original Halloween (1978) and they all returned for this sequel. The characters of Tommy Doyle and Lonnie Elam from the original also returned, but were recast with Anthony Michael Hall and Robert Longstreet. Brian Andrews retired from acting in 2015 and Brent Le Page never acted again after the original Halloween.

The firefighters perform a full smoke dive to the burning building at the start of the film, in spite of it already being up in flames and without knowledge of any survivors trapped inside. Normally, fire brigades don't endanger their people needlessly in such situations and focus only on preventing the fire from spreading to the surrounding area.

After the release of the film, director David Gordon Green announced an extended cut which would feature additional scenes and an alternate ending. In that cut (simply titled Extended Cut), Laurie would call Karen's phone near the end of the film. She is instead replied with Michael's heavy breathing, indicating Karen is dead. Laurie then leaves the hospital with a knife, determined to find him. This indicates the sequel Halloween Ends (2022) would take place immediately after Kills in 2018, instead of four years later in 2022 which would later be confirmed. The Extended Cut runs for 109 minutes.

Edited from Halloween (1978)