While in the elevator, the crew exchange between them all the lines Lando Calrissean and Darth Vader shared at the end of episode V The Empire Strikes Back
While the look of the series is very much based on the original trilogy, Dave Filoni thought it would be appropriate that the Inquisitor character should be an alien who was developed for the Prequels. At first he was going to be a Chagrian like Mas Amedda, first seen in Star Wars: Episode I - The Phantom Menace (1999). But the enormous horns associated with that species would have made it impossible to fit him into a TIE fighter. Eventually the Pau'an species from Star Wars: Episode III - Revenge of the Sith (2005) was chosen.
The Inquisitor's lightsaber is based on unused concept art from Star Wars: The Force Unleashed (2008). The same design had also previously been packaged with a General Grievous action figure.
The Phantom has an early version of Mythosaur skull seen on Boba Fett's armor (without the horns) on both sides of it's hull.