My script where ur arm gets hardened works in studio but not in game.. Why does this happen?

This does not work in game but in studio it works perfectly.. Idk what's wrong I've tried many solutions but idk...

BTW, ITS A LOCALSCRIPT.

PROBLEM: When I check in game logs I see something about the data model (client log)

"attempt to index local "char"

PLZ HELP!

Players = game.Players.LocalPlayer
mouse = Players:GetMouse()
local char = Players.Character
local torso = char:findFirstChild("Torso")
local leftarm = char:findFirstChild("Left Arm")

enabled = true

function onKeyDown(key)
	key = key:lower()
	if key == 'q' then
		local part = char["Left Arm"]:Clone()
		part.BrickColor = BrickColor.new("Institutional white")
		part.Material = "Neon"
		part.Name = "LeftArm2"
		part.CFrame = leftarm.CFrame
		part.Anchored = true
		part.CanCollide = false
		wait()
		part.Parent = char
		for i = 1, 10 do
			part.Size = part.Size +Vector3.new(0.1,0.1,0.1)
			part.Transparency = part.Transparency + 0.1
			part.CFrame = leftarm.CFrame
			wait()
		end
		part:destroy()
		torso.Anchored = true
		leftarm.BrickColor = BrickColor.new('Really black')
		leftarm.Material = 'Neon'
		leftarm.Reflectance = 0.1
		torso.Anchored = false
	end
end

enabled = false

mouse.KeyDown:connect(onKeyDown)