Book of Demons is a deck-building game that lets you decide the length of the quests that you embark on. The game was developed and published by Thing Trunk on December 13th, 2018.

There are no magical weapons in this game, only magic cards that you will use to defeat the armies of darkness that are located in the dungeons below the Old Cathedral. Only you can stop the Archdemon that wants to take over the Paperverse! Everything in the game that you can use is a card that you have to use in the best way possible. These cards can then be upgraded by runes that give many different kinds of bonuses. Thanks to the Flexiscope engine, players have the option of dividing the game into sessions of their own choosing. Over time this system learns your own pace of gaming and starts to predict the time that you're going to need in order to complete the next session.

Book of Demons has simplified movement and fight mechanics but puts a larger emphasis on timing, card selection, and order of execution, and how you pull these things off will determine your skill level in a title like this. Gameplay has been designed to be friendly and enjoyable, so you will always find points of interest marked at the top of your screen. The player's character leaves footprints on the ground that can be tracked back to your starting point. There is even a Roguelike mode that has permadeath, restricted healing, and all kinds of challenges for players that like their games hard.