By Sight

Lesson 14 of 20 in Coddy's Roblox Game: Escape the Dark course.

The monster still knows where you are through walls. A hunter only knows what it sees: a ray from its head that hits you means it sees you, and it remembers where. When it loses sight of you, it goes to where it last saw you; there, if you are gone, it gives up.

local hit = workspace:Raycast(from, character.HumanoidRootPart.Position - from, params)
return hit ~= nil and hit.Instance:IsDescendantOf(character)

With nobody to follow it patrols: the middle of the room players are in, then two rooms back, back and forth. That gives you a chance to slip past, and gives it a chance to find you.

Challenge

Medium

Write canSee(shadow, character): a ray from its Head to the character's root, leaving the monster out, that hits the character.
Write patrolPoint(back): the middle (12 studs in) of the room numbered count - 1 - back, or nil.
In runMonster: a character it cannot see does not count; one it sees sets lastSeen. Walk to the character or to lastSeen (forgetting it on arrival); with neither, walk the patrol, switching back between 0 and 2 at each point.

Press Play, then Check.

Try it yourself

local Players = game:GetService("Players")
local ServerStorage = game:GetService("ServerStorage")
local Lighting = game:GetService("Lighting")
local TweenService = game:GetService("TweenService")
local PathfindingService = game:GetService("PathfindingService")
local Settings = require(game.ReplicatedStorage.Settings)

local rooms = workspace.Rooms
local lastRoom = rooms.Lobby -- the newest room
local count = 0 -- rooms made so far
local monster = nil

-- Night falls: no sun, a little light everywhere, and fog
Lighting.ClockTime = Settings.ClockTime
Lighting.Ambient = Settings.Ambient
Lighting.OutdoorAmbient = Settings.Ambient
Lighting.FogColor = Color3.new(0, 0, 0)
Lighting.FogEnd = Settings.FogEnd
print("Lights out")

-- A tool a player carries: in their hand, or in their Backpack
local function findTool(player, name)
	return (player.Character and player.Character:FindFirstChild(name)) or player.Backpack:FindFirstChild(name)
end

-- Swing a door open on its hinge
local function openDoor(door)
	door:SetAttribute("Open", true)
	door.Panel.Prompt.Enabled = false
	local hinge, panel = door.Hinge, door.Panel
	local goal = hinge.CFrame * CFrame.Angles(0, math.rad(90), 0) * hinge.CFrame:ToObjectSpace(panel.CFrame)
	TweenService:Create(panel, TweenInfo.new(0.6), { CFrame = goal }):Play()
end

-- The nearest living player it could catch (not hidden), within MonsterSight, and how far
local function nearestCharacter(position)
	local best, bestDistance = nil, Settings.MonsterSight
	for _, player in Players:GetPlayers() do
		local character = player.Character
		local root = character and character:FindFirstChild("HumanoidRootPart")
		if root and character.Humanoid.Health > 0 and not character:GetAttribute("Hidden") then
			local distance = (root.Position - position).Magnitude
			if distance < bestDistance then
				best, bestDistance = character, distance
			end
		end
	end
	return best, bestDistance
end

-- Walk toward a point: straight when the way is clear, else along a path
local function walkToward(shadow, goal, path)
	local root = shadow.HumanoidRootPart
	local params = RaycastParams.new()
	params.FilterDescendantsInstances = { shadow }
	local hit = workspace:Raycast(root.Position, goal - root.Position, params)
	if not hit or hit.Instance.Parent:FindFirstChildOfClass("Humanoid") then
		shadow.Humanoid:MoveTo(goal)
		return
	end
	path:ComputeAsync(root.Position, goal)
	local points = path:GetWaypoints()
	if path.Status == Enum.PathStatus.Success and points[2] then
		shadow.Humanoid:MoveTo(points[2].Position)
	end
end

-- The monster's mind: every quarter second, after someone
local function runMonster(shadow)
	local humanoid = shadow.Humanoid
	local root = shadow.HumanoidRootPart
	local path = PathfindingService:CreatePath()
	while shadow.Parent do
		local character = nearestCharacter(root.Position)
		if character and (character.HumanoidRootPart.Position - root.Position).Magnitude <= Settings.CatchDistance then
			-- caught: the player is beaten, and the monster goes until the next door
			character.Humanoid.Health = 0
			shadow:Destroy()
			monster = nil
			return
		end
		if character then
			walkToward(shadow, character.HumanoidRootPart.Position, path)
		else
			humanoid:MoveTo(root.Position)
		end
		task.wait(0.25)
	end
end

-- The monster comes in behind you: at the entrance of the room two before the newest
local function spawnMonster()
	local behind = nil
	for _, room in rooms:GetChildren() do
		if room:GetAttribute("Number") == count - 2 then
			behind = room
		end
	end
	if not behind then
		return
	end
	monster = ServerStorage.Shadow:Clone()
	monster:PivotTo(behind.Entrance.CFrame + Vector3.new(0, 3.1, 0))
	monster.Humanoid.WalkSpeed = Settings.MonsterSpeed
	monster.Parent = workspace
	task.spawn(runMonster, monster)
end

local addRoom -- written below: a door adds a room, and a room has a door

-- What a door does when a player opens it
local function setupDoor(door)
	door.Panel.Prompt.Triggered:Connect(function(player)
		if door:GetAttribute("Open") then
			return
		end
		if door:GetAttribute("Locked") then
			local key = findTool(player, "Key")
			if not key then
				return
			end
			key:Destroy()
			door:SetAttribute("Locked", nil)
		end
		if door.Parent == lastRoom then
			addRoom()
		end
		openDoor(door)
	end)
end
setupDoor(workspace.Rooms.Lobby.Door)

-- Walking into a room: it becomes the player's Room, and their checkpoint
local function setupEntry(room)
	room.Entry.Touched:Connect(function(hit)
		local player = Players:GetPlayerFromCharacter(hit.Parent)
		if player then
			local number = room:GetAttribute("Number")
			player.leaderstats.Room.Value = number
			player.RespawnLocation = room.Checkpoint
		end
	end)
end
setupEntry(workspace.Rooms.Lobby)

-- A closet: E to hide inside, E again to come out
local function setupCloset(closet)
	closet.Front.Prompt.Triggered:Connect(function(player)
		local character = player.Character
		if character:GetAttribute("Hidden") then
			character:PivotTo(closet.Front.CFrame * CFrame.new(-3, -1, 0) * CFrame.Angles(0, math.rad(90), 0))
			character:SetAttribute("Hidden", nil)
		else
			character:PivotTo(closet.Inside.CFrame + Vector3.new(0, 2.5, 0))
			character:SetAttribute("Hidden", true)
		end
	end)
end

-- A new room at the exit of the newest one
function addRoom()
	count += 1
	local name = Settings.Order[(count - 1) % #Settings.Order + 1]
	if count >= Settings.RoomsToEscape then
		name = "Exit"
	end
	local room = ServerStorage.Rooms[name]:Clone()
	room:PivotTo(lastRoom.Exit.CFrame)
	room:SetAttribute("Number", count)
	room.Sign.SurfaceGui.Number.Text = "Room " .. count
	room.Parent = rooms
	lastRoom = room
	setupDoor(room.Door)
	setupEntry(room)
	-- a locked room keeps its key inside
	local keySpot = room:FindFirstChild("KeySpot")
	if keySpot then
		local key = ServerStorage.Key:Clone()
		key.Handle.CFrame = keySpot.CFrame
		key.Parent = room
		key.Handle.Prompt.Triggered:Connect(function(player)
			key.Handle.Prompt.Enabled = false
			key.Parent = player.Backpack
		end)
	end
	local closet = room:FindFirstChild("Closet")
	if closet then
		setupCloset(closet)
	end
	-- keep the newest room and KeepRooms behind it
	for _, old in rooms:GetChildren() do
		if old:GetAttribute("Number") < count - Settings.KeepRooms then
			old:Destroy()
		end
	end
	if count >= Settings.MonsterFrom and not monster then
		spawnMonster()
	end
	return room
end

-- Out of the closet, you are not hidden any more
task.spawn(function()
	while true do
		task.wait(0.25)
		for _, player in Players:GetPlayers() do
			local character = player.Character
			if character and character:GetAttribute("Hidden") then
				local closest = math.huge
				for _, inside in workspace.Rooms:GetDescendants() do
					if inside.Name == "Inside" then
						closest = math.min(closest, (inside.Position - character.HumanoidRootPart.Position).Magnitude)
					end
				end
				if closest > 4 then
					character:SetAttribute("Hidden", nil)
				end
			end
		end
	end
end)

-- Every player: Room on the leaderboard, and a flashlight every life
Players.PlayerAdded:Connect(function(player)
	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player

	local room = Instance.new("IntValue")
	room.Name = "Room"
	room.Parent = leaderstats

	player.CharacterAdded:Connect(function()
		local flashlight = ServerStorage.Flashlight:Clone()
		flashlight.Parent = player.Backpack
		local beam = flashlight.Handle.Beam
		flashlight.Activated:Connect(function()
			beam.Enabled = not beam.Enabled
		end)
	end)
end)