"It's a good thing I've had a bit of training outside my days as Moody's disciple, then." Remus laughed, not bothering to mention he normally wouldn't have added the stipulation on broken bones had they not been in the middle of a war.
When he'd first come back from the dead, Remus had spent a great deal of time reading his own history, learning what he'd done in later years. What he'd learned was that he wasn't nearly as well prepared to face the coming war as he'd thought. His future self had come out of battles without a scratch when others like Kingsley and Moody had suffered serious injury, and Sirius had died. Remus had then spent weeks, months, trying to turn himself into that man -- or, at least, that fighter.
But, as he faced off against Harry, he realised he wasn't that fighter. He was better.
While he might not have that level of experience still, he had a great deal more confidence in himself and his abilities. More than skill, more than special abilities gifted him by his curse, it was that confidence that made each move feel more natural, flow more instinctively as they made their opening shots.
Though it wouldn't happen in a real battle this way, they were feeling each other out, testing weaknesses, tells and Remus used that, sticking to routine offensive spells and standard shields he taught his trainees. He wasn't truly aware of the trainees and watchers himself. He simply moved, ducking here, stepping out of the way there, blocking and attacking with the lazy confidence of the predator he was still only truly discovering in himself.