Simple Fly

local player = game.Players.LocalPlayer
    local character = player.Character or player.CharacterAdded:Wait()
    local humanoidRootPart = character:WaitForChild("HumanoidRootPart")
    local humanoid = character:WaitForChild("Humanoid")
    local userInputService = game:GetService("UserInputService")
    local runService = game:GetService("RunService")
    local camera = game.Workspace.CurrentCamera

    local flying = false
    local baseSpeed = 150
    local maxSpeed = 250
    local acceleration = 5
    local currentSpeed = 0
    local lastDirection = nil
    local deceleration = 10
    local bodyVelocity


    local function toggleFly()
        flying = not flying
        if flying then

            bodyVelocity = Instance.new("BodyVelocity")
            bodyVelocity.MaxForce = Vector3.new(1e6, 1e6, 1e6)
            bodyVelocity.P = 1250
            bodyVelocity.Velocity = Vector3.zero
            bodyVelocity.Parent = humanoidRootPart
            currentSpeed = baseSpeed
        else

            if bodyVelocity then
                bodyVelocity:Destroy()
                bodyVelocity = nil
            end
            humanoid:ChangeState(Enum.HumanoidStateType.GettingUp)
            lastDirection = nil
        end
    end


    userInputService.InputBegan:Connect(function(input, gameProcessed)
        if gameProcessed then return end
        if input.KeyCode == Enum.KeyCode.X then
            toggleFly()
        end
    end)


    runService.RenderStepped:Connect(function(deltaTime)
        if flying and bodyVelocity then
            local moveDirection = Vector3.new(0, 0, 0)
            local currentDirection = nil

            if userInputService:IsKeyDown(Enum.KeyCode.W) then
                moveDirection = moveDirection + camera.CFrame.LookVector
                currentDirection = "W"
                if lastDirection == "S" then
                    currentSpeed = math.max(currentSpeed - deceleration * deltaTime, baseSpeed)
                end
            end
            if userInputService:IsKeyDown(Enum.KeyCode.S) then
                moveDirection = moveDirection - camera.CFrame.LookVector
                currentDirection = "S"
                if lastDirection == "W" then
                    currentSpeed = math.max(currentSpeed - deceleration * deltaTime, baseSpeed)
                end
            end
            if userInputService:IsKeyDown(Enum.KeyCode.A) then
                moveDirection = moveDirection - camera.CFrame.RightVector
                currentDirection = "A"
            end
            if userInputService:IsKeyDown(Enum.KeyCode.D) then
                moveDirection = moveDirection + camera.CFrame.RightVector
                currentDirection = "D"
            end

            if moveDirection.Magnitude > 0 then
                if currentDirection ~= lastDirection and not ((currentDirection == "W" and lastDirection == "S") or (currentDirection == "S" and lastDirection == "W")) then
                    currentSpeed = baseSpeed
                end
                currentSpeed = math.min(currentSpeed + acceleration * deltaTime, maxSpeed)
                bodyVelocity.Velocity = moveDirection.Unit * currentSpeed
                lastDirection = currentDirection
            else
                bodyVelocity.Velocity = Vector3.zero
            end


            local cameraLookVector = camera.CFrame.LookVector
            humanoidRootPart.CFrame = CFrame.new(humanoidRootPart.Position, humanoidRootPart.Position + cameraLookVector)
        end
    end)