Dreaming Mary is an original adventure game in a sidescrolling format, made using the free RPG Maker VX Ace Lite. It is inspired by the Japanese horror game Ib and the abstract game Yume Nikki, and is influenced by the indie platformer Eversion as well as the TV show Mahou Shoujo Madoka Magica. Despite these influences, Dreaming Mary is not exactly a horror game. It does contain horror elements, though they might never be encountered by a player who chooses to indulge in the dreams instead of investigating.

The game's average playtime ranges from fifteen to twenty-five minutes to reach one ending, and there are four endings. In the game you are able to interact with items and NPCs. It is important to pay attention to dialogue and to your surroundings in order to proceed. Sound is vital in this game and can help the player move forward as well as provide hints to the situation Mary has found herself in.

Mary is a girl who loves to dream. In fact, she loves to dream so much she can spend an entire day dreaming. One day, when she falls asleep, she finds herself in a nostalgic place very different from her other dreams. Everyone there knows her and treats her like an old friend, and they invite her to play with them or help them. When she finishes all of their tasks, she is invited deeper into the dream.