Fog is a Yume Nikki fangame. From the Nexus, the dreamer can explore several different dream worlds. Within the dream world, they can collect various effects and perks, which can be equipped to raise certain stats which may affect their dreams. FOG includes various puzzles throughout the dream world. Those puzzles are generally based on various visual and audio cues; solving them may reveal Effects and Perks. The game takes place in November 1998, following the lucid dreaming exploits of Leon, Tegan, and Emory as they explore their shared but corrupted dream world after their friendship fell apart. They may find ghosts of each other, as well as recurring antagonists such as Fedoras and Shadow Creatures. Although FOG has no dialogue, Leon, Tegan, and Emory may find messages visually encoded as numbers, colors, or shapes or audial encoding such as Morse code.