In Nightmare is a narrative-driven horror adventure game that combines stealth action with diverse puzzles. Players follow a young boy named Bill, who escapes into a dark, whimsical dream world created from his memories as he copes with the effects of a broken family. His past trauma manifests as terrifying monsters that seek to trap him in this twisted nightmare. Guided by a friendly ethereal "dream spirit," Bill must navigate a surreal labyrinth created by his subconscious, solve intricate puzzles, and use the environment to evade phantoms and uncover what truly lies within his mind.