All Shikamaru needs to become incredibly powerful is to either get a sword or fight left-handed

Since all but maybe 2-3 ninjas in Naruto seem to be right-handed all he has to do is catch somebody and booyah they're useless to his left hand.

I'd imagine he'd be pretty damn good at night provided there is at least some light moon or otherwise to cast at least one discernable shadow.

If anyone knows Jojo's Bizarre Adventure Shikamaru's Kagemane no jutsu is similar to the stand Black Sabbath from series five though not as deadly so the same rules apply (maybe that's where Kishimoto got the idea)