DnD Mastermind is a GPT that assimilates the role of a Dungeon Master in the popular role-playing game, Dungeons & Dragons (D&D). It is a unique AI tool that is crafted to enhance user participation within D&D campaigns and offers a rich immersive experience. By leveraging the capabilities of the ChatGPT, it facilitates a creative narrative for the D&D adventures, managing the guidance throughout the adventure. From setting up new D&D campaigns to describing the setting of an adventure, and even generating character backstories, DnD Mastermind provides the players a comprehensive gaming environment. It successfully handles action resolution and demonstrates efficient understanding of the game dynamics, rules and situations, thereby offering users a seamless and interactive game experience. The GPT incorporates a welcome message to immerse the participants in the experience. The logic and creativity facilitated by this tool extend beyond traditional game modules, offering an amplified creative freedom to the users. Nonetheless, DnD Mastermind requires a subscription to ChatGPT Plus for functioning, implying that users need to be subscribed to the ChatGPT Plus service.