According to Dee Bradley Baker, the ending of "The Wrong Jedi" was kept a secret from all the voice actors except Ashley Eckstein and Matt Lanter. The other actors all received a script in which the final page was left blank and were asked to leave the studio when it came time to record the final scene. Baker did not find out what happened until it aired on television.
The Jedi Temple guards use double sided lightsabers which for the first time in the official canon emit yellow blades. A yellow blades had been used in the Kenner Toy line for the very first Luke Skywalker action figure in 1987 and many different colored blades appeared in varous Dark Horse comics before Attack of the Clones established that Jedi generally only used blue and green blades (Mace Windu being an exception).
First episode where Tim Curry is credited as Chancelor Palpatine after original actor Ian Abercrombie's death. Curry went uncredited in both S5E1 "Revival" and S5E20 "The Lawless" for individual lines of dialogue.