JoinedChat

--ServerScriptService

local PlayerJoinedEvent = game.ReplicatedStorage.PlayerJoinedEvent

game.Players.PlayerAdded:Connect(function(Player)
    PlayerJoinedEvent:FireAllClients(Player.Name)
end)

--StarterPlayerScripts

local PlayerJoinedEvent = game.ReplicatedStorage.PlayerJoinedEvent

PlayerJoinedEvent.OnClientEvent:Connect(function(Player)
    game:GetService("StarterGui"):SetCore("ChatMakeSystemMessage",{
        Text = Player.." has joined game",
        Font = Enum.Font.SourceSansBold,
        TextSize = 24,
        Color = Color3.new(0,1,0)
    })
end)