Stygian: Reign of the Old Ones is a role-playing game set in a hand-drawn 2D world inspired by Lovecraftian themes. Players embark on a journey from a doomed Arkham into the Abyss, creating characters based on 1920's archetypes with unique backstories and abilities. The game emphasizes strategic turn-based combat, where physical confrontations and spellcasting come with significant risks, including the strain on the character's sanity. Players must navigate a broken world filled with abominations and make choices that impact their journey.

The game features a rich narrative with quests inspired by Lovecraft's works, allowing players to experience stories influenced by their decisions. Companions with bizarre backgrounds join the player’s quest, enhancing the gameplay experience. A unique Belief System influences how characters handle the warped reality of Arkham, providing diverse dialogue options. The spell system is intricate, often demanding sacrifices from players, making mastery of the occult a challenging yet rewarding endeavor.