How to make a pet follow the player in Roblox (Luau script)

-- Script in ServerScriptService (sketch): the server owns what is equipped
local Players = game:GetService("Players")

local function setEquipped(player: Player, petNames: { string })
	-- validate against the player's saved inventory before this line
	player:SetAttribute("EquippedPets", table.concat(petNames, ","))
end

Players.PlayerAdded:Connect(function(player)
	setEquipped(player, { "BatRay", "GhostJelly" }) -- load these from your save data
end)

-- LocalScript in StarterPlayer > StarterPlayerScripts
-- Draws the equipped pets of every player on this device and moves them each frame.
local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")
local RunService = game:GetService("RunService")

local PetModels = ReplicatedStorage:WaitForChild("PetModels")

local RADIUS = 4 -- studs from the player to each pet
local FOLLOW_SPEED = 10 -- higher = snappier
local FLY_HEIGHT = 2.5 -- extra height for pets with a Flying attribute
local BOB_HEIGHT = 0.35 -- studs up and down
local BOB_RATE = 0.6 -- bobs per second
local DRAW_DISTANCE = 150 -- skip pets this far from the camera

local active = {} -- [Player] = { { model, base, flying } }

local function prepare(model: Model)
	for _, part in model:GetDescendants() do
		if part:IsA("BasePart") then
			part.Anchored = true -- moved by this script, not by physics
			part.CanCollide = false
			part.CanTouch = false
			part.CanQuery = false
		end
	end
end

local function clear(player: Player)
	for _, pet in active[player] or {} do
		pet.model:Destroy()
	end
	active[player] = nil
end

local function build(player: Player)
	clear(player)
	local equipped = player:GetAttribute("EquippedPets")
	if typeof(equipped) ~= "string" or equipped == "" then
		return
	end
	local character = player.Character
	local root = character and character:FindFirstChild("HumanoidRootPart")
	local start = if root then root.CFrame else CFrame.identity
	local list = {}
	for _, name in string.split(equipped, ",") do
		local template = PetModels:FindFirstChild(name)
		if template then
			local model = template:Clone()
			prepare(model)
			model:PivotTo(start)
			model.Parent = workspace
			table.insert(list, { model = model, base = start, flying = template:GetAttribute("Flying") == true })
		end
	end
	active[player] = list
end

local function watch(player: Player)
	player:GetAttributeChangedSignal("EquippedPets"):Connect(function()
		build(player)
	end)
	player.CharacterAdded:Connect(function()
		build(player)
	end)
	build(player)
end

for _, player in Players:GetPlayers() do
	watch(player)
end
Players.PlayerAdded:Connect(watch)
Players.PlayerRemoving:Connect(clear)

RunService.PreRender:Connect(function(dt)
	local camera = workspace.CurrentCamera
	local alpha = 1 - math.exp(-FOLLOW_SPEED * dt) -- same feel at 30 or 240 fps
	local now = os.clock()
	for player, list in active do
		local character = player.Character
		local root = character and character:FindFirstChild("HumanoidRootPart")
		local humanoid = character and character:FindFirstChildOfClass("Humanoid")
		if not root or not humanoid then
			continue
		end
		if (root.Position - camera.CFrame.Position).Magnitude > DRAW_DISTANCE then
			continue
		end
		-- R15: the root part's bottom is HipHeight above the ground
		local ground = -(humanoid.HipHeight + root.Size.Y / 2)
		local count = #list
		for i, pet in list do
			local angle = (i - 1) / count * math.pi * 2 -- even circle; pet 1 sits right behind
			local offset = Vector3.new(math.sin(angle) * RADIUS, ground, math.cos(angle) * RADIUS)
			local bob = 0
			if pet.flying then
				offset += Vector3.new(0, FLY_HEIGHT, 0)
				bob = math.sin((now * BOB_RATE + i / count) * math.pi * 2) * BOB_HEIGHT
			end
			local target = root.CFrame * CFrame.new(offset)
			pet.base = pet.base:Lerp(target, alpha)
			pet.model:PivotTo(pet.base + Vector3.new(0, bob, 0))
		end
	end
end)

-- Swap the offset line in the loop above for one of these.
-- Arc behind the player: pets fan out instead of surrounding them.
local SPREAD = math.rad(35) -- angle between neighbours
local function arcSlot(i: number, count: number): Vector3
	local angle = (i - (count + 1) / 2) * SPREAD
	return Vector3.new(math.sin(angle) * RADIUS, 0, math.cos(angle) * RADIUS)
end

-- Rows of three behind the player, for big equip limits.
local function gridSlot(i: number): Vector3
	local column = (i - 1) % 3 - 1 -- -1, 0, 1
	local row = math.floor((i - 1) / 3)
	return Vector3.new(column * 3, 0, RADIUS + row * 3)
end

-- Script in ServerScriptService: physics follow with AlignPosition + AlignOrientation.
-- No per-frame loop: the constraints pull the pet toward an attachment on the player.
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local PetModels = ReplicatedStorage:WaitForChild("PetModels")
local petFolder = workspace:FindFirstChild("Pets") or Instance.new("Folder")
petFolder.Name = "Pets"
petFolder.Parent = workspace

local function spawnPet(player: Player, petName: string, offset: Vector3): Model?
	local character = player.Character
	local root = character and character:FindFirstChild("HumanoidRootPart")
	local template = PetModels:FindFirstChild(petName)
	if not root or not template then
		return nil
	end

	local pet = template:Clone()
	local primary = pet.PrimaryPart
	for _, part in pet:GetDescendants() do
		if part:IsA("BasePart") then
			part.Anchored = false
			part.CanCollide = false
			part.CanTouch = false
			part.CanQuery = false
			part.Massless = part ~= primary -- extra parts (welded to primary) add no mass
		end
	end

	local slot = Instance.new("Attachment") -- the spot the pet chases
	slot.Name = "PetSlot"
	slot.Position = offset
	slot.Parent = root

	local hold = Instance.new("Attachment")
	hold.Parent = primary

	local align = Instance.new("AlignPosition")
	align.Mode = Enum.PositionAlignmentMode.TwoAttachment
	align.Attachment0 = hold
	align.Attachment1 = slot
	align.Responsiveness = 25
	align.MaxForce = math.huge
	align.Parent = primary

	local turn = Instance.new("AlignOrientation")
	turn.Mode = Enum.OrientationAlignmentMode.TwoAttachment
	turn.Attachment0 = hold
	turn.Attachment1 = slot
	turn.Responsiveness = 20
	turn.MaxTorque = math.huge
	turn.Parent = primary

	pet:PivotTo(root.CFrame * CFrame.new(offset))
	pet.Parent = petFolder
	primary:SetNetworkOwner(player) -- the owner simulates it next to their character: smooth for them
	return pet
end

return spawnPet