The handheld device Sabine Wren plugs the droids head into in the hospital is an old retro games console called Galaxy Invader CGL from 1978. For filming, she holds it upside down.
David Tennant reprises his role as Huyang in this series. In addition to voicing Huyang in this series, he was also the voice of Huyang in Huyang's 2-episode arc in "Star Wars: The Clone Wars" for which he won a Daytime Emmy.
Before the collapse of the Jedi Order, Huyang had been training younglings for over 25,000 years (making it extraordinary that he's still 75% original parts). And while nobody's sure of his exact origins, there was a rumor that spread among the younglings that he arrived in a big blue box. This is a reference to the TARDIS in Doctor Who (2005), which takes the form of a 1950s blue police call box, where David Tennant (the voice of Huyang) played the tenth and fourteenth Doctors.
The music that plays during the end credits is called "Sabine's Suite" and was first introduced in season 3 of "Star Wars Rebels" during to episode "Trials of the Darksaber"