Kelly and Brock Burton are a young couple that moved to a house haunted by ghosts. As they pack up and run in terror from the place, they meet Milton Hobblepop, a paranormal investigator for hire. They ask him to get rid of the wraiths, using his many gadgets to detect and capture the souls on each room of the place.
Mishap: An Accidental Haunting is a hidden object game, where the main goal is to find and click on all the items listed at the bottom of the screen on the many haunted rooms of the house. Each chapter starts on a central location, that has to be scrolled horizontally to show its full extent and all its scattered objects. Several doors and other openings give access to other rooms, each with a separate list of objects and ghosts to be found. The hint button highlights the position of one of the list items, requiring four items to be collected after use to fully recharge. Instead of the static scenes common to the genre, the screens are filled with little animations showing possessed objects moving and jumping around.
Besides finding all the list entries, the player has to exorcise all the ghosts hiding on each room, by using the special monocle besides the list. When activated, the monocle becomes the cursor and covers the screen with a green filter, replacing the list with a meter showing how close the cursor is to the hiding entity. Each soul has to be found and clicked three times to be exorcised. The biographies of exorcised ghosts are added to a list with details about their former lives.
At the end of each chapter, the player has to find an extra place by deciphering a rebus puzzle, where words are combined with pictures of collected objects to complete a clue about the secret area. Afterwards, the final challenge is to complete three rounds of an arcade mini-game based on the personality of the main ghost. In the bedroom chapter, the objective is to snap photos of a bloated B-movie actress every time she suddenly materializes on the corners of the central room. Extra points are awarded for head shots. Later rounds add a rival starlet that keeps appearing to distract the player and induct wrong clicks. In the kitchen area, the mini-game is a cooking challenge, where a recipe has to be prepared for the ghost of a failed chef.