Workspace.Script:3: attempt to index field 'Character' (a nil value)
game.Players.PlayerAdded:Connect(function(player)
local Player = game.Players.LocalPlayer
player.Character.Humanoid.MaxHealth = 1000000000000000000
player.Character.Humanoid.Health = 1000000000000000000
end)

2 comments
You should have removed the LocalPlayer bit, since it is nil on the server and is redundant because you already have player defined.
I don't want to change anything to his script which may otherwise be useful to him