The Shadow Man is the final 'antagonist' you face in Act 3. He is not a physical entity you can interact with or trap, but rather a manifestation of the Neighbor's guilt and trauma. This encounter is a pure chase sequence, designed to be a frantic and terrifying escape.
Strategy: Run and React
When the Shadow Man appears, your only option is to run. There are no items that can stop him, and attempting to hide will only delay the inevitable. The path is generally linear, but it's filled with obstacles, collapsing floors, and tight corridors. You'll need to sprint constantly (Shift key) and be prepared to jump (Spacebar) over gaps or slide (Crouch while sprinting) under low obstacles. The key is to react quickly to the environment. The game will often provide visual cues for where to go next, such as glowing pathways or open doors. Don't hesitate; keep moving forward.
Environmental Awareness
Despite the panic, try to maintain some environmental awareness. Sometimes, a path might seem blocked, but a quick glance will reveal a hidden vent or a destructible wall. The Shadow Man's presence is indicated by a distorted visual effect and a menacing soundscape, which intensifies as he gets closer. If you get caught, you'll be reset to the beginning of that chase sequence. Practice makes perfect for this final gauntlet. Learn the layout of the escape route and anticipate the obstacles to make it through to the game's conclusion.