Decktective: Nightmare in the Mirror is a co-operative investigation game, featuring a 3D crime scene. Players must solve a mysterious case. They 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, players must answer several questions: Each correct answer is worth points. The more points they get, the better their outcome.

On their turn, players 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 has a value from 1 to 10 in the upper left corner. A card can 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.