Dynamic persistent leaderstats via DataStore. (ModuleScript in Roblox Studio).

LeaderstatsDataStoreManager.lua

local DataStoreService = game:GetService("DataStoreService")
local leaderstatsDataStore = DataStoreService:GetDataStore("Leaderstats")

local Self = {}

function Self.add(player)
	local success, leaderstatsData = pcall(function()
		return leaderstatsDataStore:GetAsync(player.UserId)
	end)
	
	if not success then
		warn(leaderstatsData)
		return
	end
	
	for name, value in leaderstatsData do
		local leaderstat = player.leaderstats:FindFirstChild(name)
		if not leaderstat then continue end
		
		leaderstat.Value = value
	end
end

function Self.remove(player)
	local success, errorMessage = pcall(function()
		local leaderstatsData = {}
		for _, leaderstat in player.leaderstats:GetChildren() do
			leaderstatsData[leaderstat.Name] = leaderstat.Value
		end
		
		leaderstatsDataStore:SetAsync(player.UserId, leaderstatsData)
	end)
	
	if not success then
		warn(errorMessage)
	end
end

game:BindToClose(function()
	for _, player in game.Players:GetPlayers() do
		Self.remove(player)
	end
	
	if game:GetService("RunService"):IsStudio() then
		task.wait(1)
	end
end)

return Self

TestExample.lua

local ChildrenManager = require(script.ChildrenManager)
local LeaderstatsDataStoreManager = require(script.LeaderstatsDataStoreManager)

game.Players.PlayerAdded:Connect(function(player)
	ChildrenManager.new(player)
	LeaderstatsDataStoreManager.add(player)
end)

game.Players.PlayerRemoving:Connect(function(player)
	LeaderstatsDataStoreManager.remove(player)
end)