In theatre you can't ad lib, so you want to pick really good material, like David Mamet or Shakespeare or whatever. You want to be really careful about what you do. But in the movies, you do have more wiggle-room. You do have more opportunities to improvise. It's fun to improvise, but I still think it's better to have a great script.
If complete and utter chaos was lightning, then he'd be the sort to stand on a hilltop in a thunderstorm wearing wet copper armour and shouting 'All gods are bastards!