It's been a long time since Stardust Dragon was a significant threat in the competitive scene, but it looks like the mighty dragon's back in action for the foreseeable future.
As always, Stardust Dragon is great at protecting whatever setup you've worked for. Stopping cards like Raigeki, Dark Hole, and Black Rose Dragon is key to protecting your board from destruction. But more importantly today, you can use Stardust Dragon to keep your Pendulum Scales safe from Wavering Eyes. As most players know, Wavering Eyes is pretty much an auto-win in the Pendulum mirror match, so preventing it from resolving is crucial.
Even cooler, you can use Stardust Dragon to stop your opponent from destroying their own cards, which is becoming increasingly popular in top decks. Wisdom-Eye Magician needs to destroy itself to place another Magician into the Pendulum Scale, and Luster Pendulum, the Dracoslayer has to destroy the opposite Pendulum Scale to get the search. Stardust Dragon's coolest function may be stopping Ignister Prominence, the Blasting Dracoslayer when it attempts to destroy a Pendulum card to shuffle away something else.
While Stardust's use has definitely shifted over the years, I'd say that it's a force to reckon with in modern competition, and you'll have to find new ways to play around it if you want to stay on the cutting edge.