Further enhance and add in good back tracking so that it'll always track the back of someone's torso and a more aesthetic GUI. ALSO layer the lock-on so that it would be more accurate and not ping dependent.

```
--[[
    Enhanced Lock-On and ESP Script with GUI for Body Part Selection and Layered Tracking
    - Allows selection of specific humanoid body parts: Left Arm, Left Leg, Torso, Torso (Back), Head, Right Leg, Right Arm.
    - Implements a layered tracking method to prioritize and manage target selections.
    - Integrates a user-friendly GUI for real-time body part selection.
    - Maintains all previous functionalities including ShiftLock support, predictive algorithms, and hitbox detection.
--]]

-- Services
local Players = game:GetService("Players")
local RunService = game:GetService("RunService")
local UserInputService = game:GetService("UserInputService")
local GuiService = game:GetService("GuiService")
local ContextActionService = game:GetService("ContextActionService")
local TweenService = game:GetService("TweenService")
local Workspace = game:GetService("Workspace")
local CurrentCamera = Workspace.CurrentCamera

-- Configuration
local DEBUG = true  -- Toggle debug logs
local ROTATION_SPEED = 25        -- Smooth rotation speed multiplier
local ESP_TEXT_PREFIX = "Targeted: " -- Prefix Text displayed in ESP
local ESP_COLOR = Color3.fromRGB(255, 0, 0)  -- Color of the ESP text
local PREDICTION_TIME_BASE = 1.1 -- Base time in seconds to predict target movement
local PREDICTION_TIME_ADJUSTMENT_FACTOR = 0.5 -- Factor to adjust prediction time based on velocity and distance
local VELOCITY_ALPHA = 0.8 -- Alpha value for Exponential Moving Average
local LOCK_ON_KEY = Enum.KeyCode.E -- Key to toggle lock-on
local SHIFT_LOCK_TOGGLE_KEY = Enum.KeyCode.LeftShift -- Key to toggle ShiftLock mode
local BACK_OFFSET = 5 -- Studs behind the target's torso to aim

-- GUI Configuration
local GUI_CONFIG = {
    ScreenGuiName = "LockOnESPGUI",
    FrameSize = UDim2.new(0, 200, 0, 300),
    FramePosition = UDim2.new(0, 10, 0.5, -150),
    ButtonSize = UDim2.new(1, 0, 0, 30),
    BodyParts = {
        "Left Arm",
        "Left Leg",
        "Torso",
        "Torso (Back)",
        "Head",
        "Right Leg",
        "Right Arm"
    },
    SelectedColor = Color3.fromRGB(0, 255, 0),
    UnselectedColor = Color3.fromRGB(255, 255, 255)
}

-- Debug Function
local function debugLog(message)
    if DEBUG then
        print("[LockOnScript]: " .. message)
    end
end

-- Variables
local player = Players.LocalPlayer
if not player then
    error("LocalPlayer not found!")
    return
end

local character = player.Character or player.CharacterAdded:Wait()
local humanoid = character:WaitForChild("Humanoid")
local humanoidRootPart = character:WaitForChild("HumanoidRootPart")
local trackedTarget = nil          -- Currently tracked target (another player)
local espIndicator = nil           -- BillboardGui for ESP
local shiftLockMode = false        -- ShiftLock mode toggle
local lockOnMode = false           -- Lock-On mode toggle
local velocityEMA = Vector3.new(0, 0, 0) -- Exponential Moving Average for target velocity
local selectedBodyPart = "Torso (Back)" -- Default selected body part

-- Determine Rig Type and set the torso part name
local isR15 = humanoid.RigType == Enum.HumanoidRigType.R15
local torsoPartName = isR15 and "UpperTorso" or "Torso"
debugLog("Rig type determined: " .. (isR15 and "R15" or "R6"))
debugLog("Torso part set to: " .. torsoPartName)

-- Mapping for R6 and R15 body parts
local bodyPartMappings = {
    ["Left Arm"] = isR15 and "LeftUpperArm" or "Left Arm",
    ["Left Leg"] = isR15 and "LeftUpperLeg" or "Left Leg",
    ["Torso"] = torsoPartName,
    ["Torso (Back)"] = torsoPartName, -- Special handling
    ["Head"] = "Head",
    ["Right Leg"] = isR15 and "RightUpperLeg" or "Right Leg",
    ["Right Arm"] = isR15 and "RightUpperArm" or "Right Arm"
}

-- Helper Function: Check if a model has a Humanoid
local function hasHumanoid(model)
    return model and model:FindFirstChildOfClass("Humanoid") ~= nil
end

-- Helper Function: Find the closest player to the local player
local function findClosestPlayer()
    local closestPlayer = nil
    local shortestDistance = math.huge

    for _, otherPlayer in ipairs(Players:GetPlayers()) do
        if otherPlayer ~= player and otherPlayer.Character and hasHumanoid(otherPlayer.Character) then
            local targetPartName = bodyPartMappings[selectedBodyPart]
            local otherTorso = otherPlayer.Character:FindFirstChild(targetPartName)
            if otherTorso and otherTorso:IsA("BasePart") then
                local distance = (otherTorso.Position - humanoidRootPart.Position).Magnitude
                if distance < shortestDistance then
                    shortestDistance = distance
                    closestPlayer = otherPlayer
                end
            end
        end
    end

    if closestPlayer then
        debugLog("Closest player found: " .. closestPlayer.Name .. " with distance " .. string.format("%.2f", shortestDistance))
    else
        debugLog("No closest player found.")
    end

    return closestPlayer
end

-- Function: Toggle Lock-On to the Closest Player when LOCK_ON_KEY is pressed
local function toggleLockOn()
    if lockOnMode then
        -- Deselect the current target
        debugLog("Deselecting current target: " .. (trackedTarget and trackedTarget.Name or "None"))
        trackedTarget = nil
        lockOnMode = false
        if espIndicator then
            espIndicator:Destroy()
            espIndicator = nil
            debugLog("ESP indicator destroyed.")
        end
    else
        -- Find and select the closest player
        local closestPlayer = findClosestPlayer()
        if closestPlayer and closestPlayer.Character then
            trackedTarget = closestPlayer.Character
            lockOnMode = true
            debugLog("Tracking new target: " .. closestPlayer.Name)
            -- Create ESP indicator
            local targetPartName = bodyPartMappings[selectedBodyPart]
            local targetPart = trackedTarget:FindFirstChild(targetPartName)
            if targetPart then
                -- Ensure previous ESP is removed
                if espIndicator then
                    espIndicator:Destroy()
                    espIndicator = nil
                    debugLog("Previous ESP indicator destroyed.")
                end

                -- Create BillboardGui for ESP
                espIndicator = Instance.new("BillboardGui")
                espIndicator.Adornee = targetPart
                espIndicator.Size = UDim2.new(0, 150, 0, 50)
                espIndicator.StudsOffset = Vector3.new(0, 2, 0)
                espIndicator.AlwaysOnTop = true
                espIndicator.Name = "TargetESP"

                -- Create TextLabel for ESP
                local textLabel = Instance.new("TextLabel")
                textLabel.Parent = espIndicator
                textLabel.Size = UDim2.new(1, 0, 1, 0)
                textLabel.BackgroundTransparency = 1
                textLabel.Text = ESP_TEXT_PREFIX .. trackedTarget.Name .. " (" .. selectedBodyPart .. ")"
                textLabel.TextColor3 = ESP_COLOR
                textLabel.Font = Enum.Font.SourceSansBold
                textLabel.TextScaled = true
                textLabel.TextStrokeTransparency = 0.8

                -- Parent the ESP to the player's PlayerGui
                local playerGui = player:WaitForChild("PlayerGui")
                espIndicator.Parent = playerGui
                debugLog("ESP indicator created for " .. closestPlayer.Name .. " targeting " .. selectedBodyPart)
            else
                debugLog("Selected body part '" .. targetPartName .. "' not found on " .. closestPlayer.Name)
                trackedTarget = nil
            end
        else
            debugLog("No valid closest player to track.")
        end
    end
end

-- Function: Predict Future Position Based on Target's Velocity using EMA
local function getPredictedPosition(targetCharacter)
    local targetPartName = bodyPartMappings[selectedBodyPart]
    local targetPart = targetCharacter:FindFirstChild(targetPartName)
    if not targetPart then
        debugLog("Target does not have the part: " .. targetPartName)
        return nil
    end

    -- Get current velocity
    local currentVelocity = targetPart.Velocity

    -- Update Exponential Moving Average (EMA) for velocity
    velocityEMA = (currentVelocity * VELOCITY_ALPHA) + (velocityEMA * (1 - VELOCITY_ALPHA))

    -- Calculate dynamic prediction time based on velocity magnitude and distance
    local distance = (targetPart.Position - humanoidRootPart.Position).Magnitude
    local velocityMagnitude = velocityEMA.Magnitude
    local predictionTime = PREDICTION_TIME_BASE + (velocityMagnitude * PREDICTION_TIME_ADJUSTMENT_FACTOR) + (distance * PREDICTION_TIME_ADJUSTMENT_FACTOR)
    predictionTime = math.clamp(predictionTime, 0.2, 0.8) -- Clamp prediction time between 0.2 and 0.8 seconds

    -- Calculate predicted position
    local futurePosition = targetPart.Position + (velocityEMA * predictionTime)
    debugLog(string.format("Predicted position: (%.2f, %.2f, %.2f); Prediction Time: %.2f", 
        futurePosition.X, futurePosition.Y, futurePosition.Z, predictionTime))

    -- Special Handling for "Torso (Back)"
    if selectedBodyPart == "Torso (Back)" then
        if velocityEMA.Magnitude > 0 then
            -- If the target is moving, assume back is opposite to their velocity
            local backDirection = -velocityEMA.Unit
            futurePosition = futurePosition + (backDirection * BACK_OFFSET)
            debugLog("Calculated back position based on movement.")
        else
            -- If the target is stationary, use their current orientation
            futurePosition = futurePosition - (targetPart.CFrame.LookVector * BACK_OFFSET)
            debugLog("Calculated back position based on orientation.")
        end
    end

    debugLog(string.format("Final target position: (%.2f, %.2f, %.2f)", futurePosition.X, futurePosition.Y, futurePosition.Z))
    return futurePosition
end

-- Function: Instantly rotate to face the predicted target position
local function instantRotateToPosition(targetPosition)
    if not targetPosition then return end

    local desiredCFrame = CFrame.new(humanoidRootPart.Position, targetPosition)
    humanoidRootPart.CFrame = desiredCFrame
    debugLog("Instantly rotated to face target position.")
end

-- Function: Smoothly rotate to face the predicted target position
local function smoothRotateToPosition(targetPosition, deltaTime)
    if not targetPosition then return end

    local direction = (Vector3.new(targetPosition.X, humanoidRootPart.Position.Y, targetPosition.Z) - humanoidRootPart.Position).Unit
    local desiredCFrame = CFrame.new(humanoidRootPart.Position, humanoidRootPart.Position + direction)

    -- Smoothly interpolate the CFrame
    humanoidRootPart.CFrame = humanoidRootPart.CFrame:Lerp(desiredCFrame, ROTATION_SPEED * deltaTime)
    debugLog("Smoothly rotated to face target position.")
end

-- Function: Rotate to Target (Instant or Smooth based on toggle)
local function rotateToTarget(deltaTime)
    if not trackedTarget then return end

    local targetPartName = bodyPartMappings[selectedBodyPart]
    local targetPart = trackedTarget:FindFirstChild(targetPartName)
    if targetPart and targetPart:IsA("BasePart") then
        local predictedPosition = getPredictedPosition(trackedTarget)
        if predictedPosition then
            if shiftLockMode then
                instantRotateToPosition(predictedPosition)
            else
                smoothRotateToPosition(predictedPosition, deltaTime)
            end

            -- Hitbox Detection: Ensure predicted position is within part bounds
            local partSize = targetPart.Size
            local partPosition = targetPart.Position
            local deltaPosition = predictedPosition - partPosition

            local withinX = math.abs(deltaPosition.X) <= (partSize.X / 2 + (selectedBodyPart == "Torso (Back)" and BACK_OFFSET or 0))
            local withinY = math.abs(deltaPosition.Y) <= (partSize.Y / 2)
            local withinZ = math.abs(deltaPosition.Z) <= (partSize.Z / 2 + (selectedBodyPart == "Torso (Back)" and BACK_OFFSET or 0))

            if withinX and withinY and withinZ then
                debugLog("Predicted position is within the part's hitbox.")
            else
                debugLog("Predicted position is outside the part's hitbox.")
            end
        else
            debugLog("Failed to get predicted target position.")
        end
    else
        debugLog("Target part '" .. targetPartName .. "' is invalid or missing.")
    end
end

-- Function: Handle ShiftLock Toggle
local function toggleShiftLock()
    if shiftLockMode then
        -- Disable ShiftLock Mode
        shiftLockMode = false
        CurrentCamera.CameraType = Enum.CameraType.Custom
        debugLog("ShiftLock mode disabled.")
    else
        if lockOnMode then
            -- Disable Lock-On before enabling ShiftLock to prevent conflicts
            toggleLockOn()
        end
        -- Enable ShiftLock Mode
        shiftLockMode = true
        CurrentCamera.CameraType = Enum.CameraType.Scriptable
        -- Lock the camera to look at the target
        if trackedTarget then
            local targetPartName = bodyPartMappings[selectedBodyPart]
            local targetPart = trackedTarget:FindFirstChild(targetPartName)
            if targetPart then
                local predictedPosition = getPredictedPosition(trackedTarget)
                CurrentCamera.CFrame = CFrame.new(humanoidRootPart.Position, predictedPosition)
                debugLog("ShiftLock mode enabled and camera locked onto target.")
            end
        end
    end
end

-- Function: Clean up ESP when the tracked target dies or leaves
local function onTrackedTargetRemoved()
    if not trackedTarget then return end
    debugLog("Tracked target removed or died: " .. (trackedTarget.Name or "Unknown"))
    trackedTarget = nil
    lockOnMode = false
    if espIndicator then
        espIndicator:Destroy()
        espIndicator = nil
        debugLog("ESP indicator destroyed due to target removal.")
    end
    velocityEMA = Vector3.new(0, 0, 0) -- Reset velocity EMA
    -- Reset camera if ShiftLock was active
    if shiftLockMode then
        toggleShiftLock()
    end
end

-- Function: Monitor Tracked Target for Removal or Death
local function monitorTrackedTarget(targetCharacter)
    if not targetCharacter then return end

    local humanoid = targetCharacter:FindFirstChildOfClass("Humanoid")
    if humanoid then
        humanoid.Died:Connect(function()
            debugLog("Tracked target " .. (targetCharacter.Name or "Unknown") .. " has died.")
            onTrackedTargetRemoved()
        end)
    end

    targetCharacter.AncestryChanged:Connect(function()
        if not targetCharacter:IsDescendantOf(game) then
            debugLog("Tracked target " .. (targetCharacter.Name or "Unknown") .. " has left the game.")
            onTrackedTargetRemoved()
        end
    end)
end

-- Modify toggleLockOn to monitor the tracked target
local originalToggleLockOn = toggleLockOn
toggleLockOn = function()
    originalToggleLockOn()
    if trackedTarget then
        monitorTrackedTarget(trackedTarget)
    end
end

-- Function: Handle Character Respawn
player.CharacterAdded:Connect(function(newCharacter)
    debugLog("Character respawned.")
    character = newCharacter
    humanoid = character:WaitForChild("Humanoid")
    humanoidRootPart = character:WaitForChild("HumanoidRootPart")
    
    -- Determine rig type using RigType property
    isR15 = humanoid.RigType == Enum.HumanoidRigType.R15
    torsoPartName = isR15 and "UpperTorso" or "Torso"
    debugLog("New rig type determined: " .. (isR15 and "R15" or "R6"))
    
    -- Reset tracking and ESP on respawn
    onTrackedTargetRemoved()
end)

-- Function: Update Camera during ShiftLock Mode
local function updateCamera(deltaTime)
    if shiftLockMode and trackedTarget then
        local targetPartName = bodyPartMappings[selectedBodyPart]
        local targetPart = trackedTarget:FindFirstChild(targetPartName)
        if targetPart then
            -- Smoothly move the camera to follow the target
            local predictedPosition = getPredictedPosition(trackedTarget)
            if predictedPosition then
                local desiredCFrame = CFrame.new(humanoidRootPart.Position, predictedPosition)
                CurrentCamera.CFrame = CurrentCamera.CFrame:lerp(desiredCFrame, ROTATION_SPEED * deltaTime)
                debugLog("Camera updated to follow target in ShiftLock mode.")
            end
        end
    end
end

-- Function: Create and Setup the Body Part Selection GUI
local function createBodyPartSelectionGUI()
    -- Check if the GUI already exists to prevent duplication
    if player.PlayerGui:FindFirstChild(GUI_CONFIG.ScreenGuiName) then
        debugLog("GUI already exists. Skipping creation.")
        return
    end

    -- Create ScreenGui
    local screenGui = Instance.new("ScreenGui")
    screenGui.Name = GUI_CONFIG.ScreenGuiName
    screenGui.Parent = player.PlayerGui
    screenGui.ResetOnSpawn = false

    -- Create Frame
    local frame = Instance.new("Frame")
    frame.Size = GUI_CONFIG.FrameSize
    frame.Position = GUI_CONFIG.FramePosition
    frame.BackgroundTransparency = 0.5
    frame.BackgroundColor3 = Color3.fromRGB(0, 0, 0)
    frame.Parent = screenGui

    -- Create UIListLayout for organized buttons
    local uiListLayout = Instance.new("UIListLayout")
    uiListLayout.Parent = frame
    uiListLayout.FillDirection = Enum.FillDirection.Vertical
    uiListLayout.SortOrder = Enum.SortOrder.LayoutOrder
    uiListLayout.Padding = UDim.new(0, 5)

    -- Function to handle body part selection
    local function selectBodyPart(bodyPart, button)
        selectedBodyPart = bodyPart
        debugLog("Selected body part: " .. bodyPart)
        toggleLockOn() -- Deselect current target
        -- Update ESP text if a target is already locked on
        if lockOnMode and espIndicator then
            espIndicator:Destroy()
            espIndicator = nil
            debugLog("ESP indicator destroyed due to body part change.")
            toggleLockOn() -- Re-select target with new body part
        end

        -- Update button colors to indicate selection
        for _, btn in ipairs(frame:GetChildren()) do
            if btn:IsA("TextButton") then
                btn.BackgroundColor3 = GUI_CONFIG.UnselectedColor
            end
        end
        button.BackgroundColor3 = GUI_CONFIG.SelectedColor
    end

    -- Create Buttons for each Body Part
    for _, bodyPart in ipairs(GUI_CONFIG.BodyParts) do
        local button = Instance.new("TextButton")
        button.Size = GUI_CONFIG.ButtonSize
        button.Text = bodyPart
        button.Font = Enum.Font.SourceSans
        button.TextSize = 18
        button.TextColor3 = Color3.fromRGB(255, 255, 255)
        button.BackgroundColor3 = (bodyPart == selectedBodyPart) and GUI_CONFIG.SelectedColor or GUI_CONFIG.UnselectedColor
        button.AutoButtonColor = false
        button.Parent = frame

        button.MouseButton1Click:Connect(function()
            selectBodyPart(bodyPart, button)
        end)
    end

    debugLog("Body Part Selection GUI created.")
end

-- Call the function to create the GUI
createBodyPartSelectionGUI()

-- Function: Setup ShiftLock and Lock-On Toggles
local function setupShiftLockToggle()
    UserInputService.InputBegan:Connect(function(input, gameProcessed)
        if gameProcessed then return end

        if input.KeyCode == LOCK_ON_KEY then
            toggleLockOn()
        elseif input.KeyCode == SHIFT_LOCK_TOGGLE_KEY then
            toggleShiftLock()
        end
    end)
end

-- Event Listeners

-- Setup ShiftLock and Lock-On Toggles
setupShiftLockToggle()

-- Render Step: Continuously update rotation and camera if a target is tracked
RunService.RenderStepped:Connect(function(deltaTime)
    if lockOnMode and trackedTarget then
        pcall(function()
            rotateToTarget(deltaTime)
            updateCamera(deltaTime)
        end)
    end

    -- Close Proximity Check Removed
    -- The handleCloseProximity function and related checks have been removed as per the latest request.
end)