Gun only working in singleplayer?

--LocalScript
local player 
local weapon = script.Parent
local mForRest
local bullet = weapon.hitter
local Var = weapon.Target

function shoot()
	local target = mForRest.Hit
	print(target)
	Var.Value = target
	
end
weapon.Equipped:connect(function(mouse)
	player = game:GetService("Players").LocalPlayer
	mForRest = mouse
	mouse.Button1Down:connect(shoot)
end)

-- Script
local target = script.Parent.Target
local bullet = script.Parent.hitter

target.Changed:connect(function(value)
	print("ShotsFired")
	local shot = bullet:Clone()
	shot.Parent = workspace
	shot.CFrame = value
	shot.Size = Vector3.new(0.2,0.2,0.2)
end)

Both scripts are located within the tool. Hitter is an instance of a part and Target is a CFrame variable to communicate between the scripts.

Anyone know why this only works in single player?

Error log

hitter is not a valid member of Tool

Use WaitForChild

You have to wait for things to load because sometimes the script loads before the objects. Example,

--LocalScript
local player 
local weapon = script.Parent
local mForRest
local bullet = weapon:WaitForChild("hitter")
local Var = weapon:WaitForChild("Target")

function shoot()
    local target = mForRest.Hit
    print(target)
    Var.Value = target

end
weapon.Equipped:connect(function(mouse)
    player = game:GetService("Players").LocalPlayer
    mForRest = mouse
    mouse.Button1Down:connect(shoot)
end)


-------------------------------------------------------

-- Script
local target = script.Parent:WaitForChild("Target")
local bullet = script.Parent:WaitForChild("hitter")

target.Changed:connect(function(value)
    print("ShotsFired")
    local shot = bullet:Clone()
    shot.Parent = workspace
    shot.CFrame = value
    shot.Size = Vector3.new(0.2,0.2,0.2)
end)

Let me know if that works for you.

Good Luck!

If I helped, please don't forget to accept my answer.