any help ServerScriptService.Main.Mob:4: attempt to index nil with 'Move' ?

usually when there's an error like attempt to index nil with ... is because it hasn't loaded in yet

you could try to use :WaitForChild(instancename, timeout) which returns the instance after it has loaded.

the parameter instance name as it implies, takes in the child name.

the parameter timeout is the time in seconds before it stops waiting until the child loads.

in your case it could be something along the lines of

local serverscriptservice = game:GetService("ServerScriptService")
local main = serverscriptservice:WaitForChild("Main")
local mob = main:WaitForChild("Mob")

now you can index the Mob instance with move without problem.

if you prefer not to use variables you could also just simply do

game:GetService("ServerScriptService"):WaitForChild("Main"):WaitForChild("Mob")

then again. this is just based off of the little information you have given to me.

if this doesn't help then please do include some code so people get better context of why exactly you're facing a problem.