Decktective: Nightmare in the Mirror is a co-operative investigation game, containing a 3D crime scene. The players must solve a mysterious case. They will play their cards to share information, discard cards that they think will lead them the wrong way, discuss the clues they find with the other players, make hypotheses and deductions to find the solution! At the end of the game, the players must answer several questions: Each correct answer is worth points. The more points they get, the better the game outcome.

On their turn, players will either play a card from their hand and put it face up on the table, sharing the information on it or they discard a card from their hand face down to the archive and are not allowed to talk about the information on it, until the end of the investigation. Each card will have a value from 1 to 10 in the upper left corner. A card may be played face up on the table only if its value is equal to or less than the current number of cards in the archive.