It's difficult to discern, but the monster in the closet is designed to look like the napalmed bodies from Vietnam with bullets for fingers.
The original screenplay by Fred Dekker was a traditional horror film with no humor at all. The comedy was all added by Ethan Wiley when he rewrote the script.
Sean S. Cunningham recalls visiting Hong Kong around the time of the film's release there, but he was confused by a poster he saw there as it featured an abundance of characters for the title. He asked why it took so many to simply say 'House', but he discovered the title had been changed to 'Don't Go Into the Haunted House After Midnight.'
According to Fred Dekker, the script was originally inspired by Twilight Zone: The Movie (1983). After seeing that film, Dekker and his friends, which included Ethan Wiley, Steve Miner, and Shane Black, planned to make their own independent anthology movie on video. But the project was never completed. Dekker used the idea for his unproduced segment for this film.
William Katt's own son visited the set on the day they filmed the scene where Roger is pulled into the closet, and the boy broke down seeing his dad in danger.