Rules: I Stay Vigil in the Mental Hospital

For internship credit, I became a night nurse at a mental hospital. The old employee only told me three rules, but I laughed at them all. Until that night, I pushed open the iron door of Ward 13 with my own hands. "I" in the mirror gave me a weird smile and said, "I got you." At the moment of death, the mysterious old man burst into the door and said: "What is locked here is not a human being, but a 'mirror puppet'." While he was still in shock, the screen of his phone automatically lit up, displaying a cold game prompt. I was forced to join the weird game of "Night Watch", and the only way to pass it was to abide by the rules that sounded the most unreasonable. Later I learned that there was an even more ancient existence suppressed underground in this hospital. And my job has changed from taking care of patients to guarding the door that must not be opened.