Although Star Wars Rebels never really managed to live up to the reputation set by its predecessor, the 2008 Clone Wars TV show, it more than made up with it by introducing a metric tonne of convincing antagonists, the most creative of which made their debut in its first season.
One such villain was the Grand Inquisitor, one of Darth Vader's Sith subordinates tasked with hunting down fugitive Jedi and... well, you get the picture. The Inquisitors were a sinister bunch, but it was their Pau'an Grand chief who was the worst of the worst, brandishing a rotating dual blade that could intimidate even the steeliest of Jedi.
It did look a tad comical when the Inquisitors used their lightsabers as their own personal helicopter, levitating into the air like a sixties Batman villain, but in combat they were fierce, intimidating and ruthless.
There's never been a lightsaber quite like it, and while there's certainly nothing wrong with your average double-bladed weapon, the rotating nature of the Inquisitor's lightsaber gives it a fear-factor few other weapons in the galaxy could match, lest they hold the capacity to wipe out an entire planet in an instant.