The Mysterious House Is the first non-canonical video tape. It was released to celebrate Halloween.
The video starts off with the logo for MW Animation Studios. The title card shows "Duckie & Tammy: THE MYSTERIOUS HOUSE".
Duckie and Tammy appear in front of some houses, complaining about the lack of candy they received on Halloween. Tammy claims it is Duckie's fault for his bad costume, while Duckie claims it is because Tammy wasn't wearing one at all. Duckie suggests going to more houses for candy. The video cuts off Tammy's agreement to a missing poster with a picture of a bear in a pumpkin costume who is named Johnny Bear, who went missing on October 31st, 1978.
Duckie and Tammy later appear in a forest celebrating their success of getting more candy. Duckie suggests returning home for the night, but Tammy dares him to visit a mysterious house in the woods. Duckie makes her promise that it would be the last house they trick-or-treat for.
The two of them are invited by Sha into the home for candy. She introduces them to her friends, and the duo receives candy from the Pumpkin Rabbit. TVA takes a picture of them and the rabbit shows them the other pictures they have taken of trick-or-treaters (There are dates written under each picture: October 31st, 1975, October 31st, 1976, October 31st, 1977, October 31st, 1978). He then insists that they stay the night in their home, which Duckie and Tammy hesitantly accepts.
Duckie and Tammy are now in sleeping bags in one of the rooms of the house. Duckie leaves the room. Some time later, Tammy wakes up and hears him call out her name. She leaves the room and finds Billy standing in the corner of the hallway. She explores further in the hallway and, unbeknownst to her, is followed by the Witch Sheep.
After some searching through some hallways and doors, she finally finds Duckie in a room. She enters the room and doesn't notice that someone closes the door. She tells Duckie to stop playing a joke with her, when his mangled body suddenly appears. She looks around the room and finds more dead bodies of children, all of whom were in pictures in the house.
The Pumpkin Rabbit comes into the room and asks Tammy why she was in the room. She frantically asks him "What have you done?", referring to the corpses. The Pumpkin Rabbit only says that he will have to punish her for wandering around the house. Tammy tells him to get away from her, but the rabbit takes off his mask, revealing a charred and disturbing face, and attacks her. Her dead body appears before the text "THE END" overlays the screen.
- The carpet seen in the Mysterious House is a reference to The Shining, a 1980 horror film.
- The wall clock in the bedroom appears to be Banny.
- It appears that some of the kids in the Mysterious House of past years somehow escaped, as two of the kids seen in the picture frames, a dog in an angel costume and a hippo, were not shown as corpses at the end.
- When Tammy discovers Duckie's corpse, The Streets of Cairo starts to play.