In part 4 of my Horror Escape Game series in Unreal Engine 5, I build a beginner-friendly Behavior Tree setup for a Ghost AI so it actually feels alive in the house. Up to this point the ghost only started moving when you entered its line of sight, but here I make it roam into random rooms using a Behavior Tree + custom AI Controller. I create a Ghost_BT, hook it up through a Ghost AI Controller (Run Behavior Tree on BeginPlay), and set Auto Possess AI to “Placed in World or Spawned” so it works even when the ghost is spawned. For roaming, I place Target Points around all floors, store them in an “Explore Points” TargetPoint array on the ghost (instant editable + expose to spawn), and then in a Roaming Task I pick a random index at runtime using array length (so I don’t hardcode values). I also add a quick check to avoid picking the same point twice, and I move the ghost using AI Move To with a small acceptance radius. After that, I introduce a proper state system using an Enum + Blackboard key (Roaming, Chasing, Lost, Attack, Follow) and decorators to switch sequences cleanly. Finally, I implement a “Lost” task that smoothly lerps the walking speed to 0 using a Blueprint Interface + Timeline, waits 5 seconds using a timer (with abort handling), and then switches back to roaming.