Lua Get/Set Metatable

local ents = {
  GetLocalPlayer = function()
  
    local tbl = {
      localplayer = {"Ava", "1", {213,234,234}},
      
      GetIndex = function(self)
        return self.localplayer[2]
      end,
    }
    setmetatable(tbl, getmetatable(tbl.localplayer))
    return tbl
  end
}

local function main()
  print(ents.GetLocalPlayer()[2])
end

main() print returns nil. If I was to do ents.GetLocalPlayer():GetIndex() however, it returns 1.

The idea is to have the default return value to be localplayer if I don't do things such as GetIndex()

A table has no default metatable, which is why your getmetatable call returns nil. In order to do anything, the second argument to setmetatable must be a table that has at least one metamethod. (__index is the most common metamethod.)

The solution is to change getmetatable(tbl.localplayer) to {__index = tbl.localplayer}.