Why Script Works In Studio But Not Online?

Problem: Title -- Local script btw

Script

local mode = 1
local sound = script:WaitForChild('Sound')
Player = script.Parent.Parent
Character = Player.CharacterAdded:wait()
leaderstats = Player:WaitForChild('leaderstats')
gold = leaderstats:WaitForChild('Running')
local PlayerGui = Player:WaitForChild('PlayerGui')

Humanoid = Character:WaitForChild('Humanoid')

mouse = Player:GetMouse()

local WalkAnim = Instance.new("Animation")
WalkAnim.AnimationId = "rbxassetid://389302210"

local SprintAnim = Instance.new("Animation")
SprintAnim.AnimationId = "rbxassetid://389349781"
run = game:GetService("RunService")

local SprintTheAnim = Humanoid:LoadAnimation(SprintAnim)




function onKeyDown(key)
    local Key = key:lower()
    if key == "r" and mode == 1 then
        print(1)
        game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 16 * 1.5
        sound:Play()
        local animationTrack = Humanoid:LoadAnimation(SprintAnim)
        animationTrack:Play()
        gold.Value = true
        mode = 2        

    elseif key == "r" and mode == 2 then
        print(3)
        game.Players.LocalPlayer.Character.Humanoid.WalkSpeed = 16
        sound:Play()
        local animationTrack = Humanoid:LoadAnimation(WalkAnim)
        animationTrack:Play()
        gold.Value = true
        mode = 1

    end

end

mouse.KeyDown:connect(onKeyDown)