Twi'lek!Vanessa has two songs, but no role in the narrative of the episode.
As per the nature of this special, the Star Wars characters make brief appearances at various points.
While trading with the Jawas, Phineas offers a Phinedroid from "I, Brobot".
Also, just like in the movie, Isabella gives Phineas a Forceful Kiss at the end.
Unlike in the movie, Perry was instead relocated off of Tatooine, and the boys still have full memory of him.
According to Phineas, his, Ferb's, and Perry's lives played out similarly to the events their primary counterparts went through in the Across the 2nd Dimension movie like his canon counterpart, Perry lived with the boys as their pet before he was outed as a spy, and the boys felt hurt and betrayed by this revelation.
Buford's hoagie pops up no less than four times.
One of the imperial Mooks talks about getting a saxophone.
Then after he escapes, he declares he'll be back to fight in the sequel.
At the end of his musical number, Darthenshmirtz tells his Stormtrooper backup dancers to stay on their comms for a potential victory song in Act IV.
Blatto gives a Spoiler alert to Phineas and Ferb after they explain the weakness of the Death Star.
The latter disarms Phineas, destroys his lightsaber, and blocks his, Perry's, and Candace's attempts to fight back. He doesn't understand why his brother is trying to hurt him, and Darth Ferb is a more ruthless fighter.
Break the Cutie: Phineas during his fight with Darth Ferb.
The Empire also did this to their Stormtroopers, though Baljeet insists that it was just orientation.
He plans to do the same to Phineas after making some modifications to the Sithinator.
Ferb is turned into Darth Ferb when he is hit by Darthenshmirtz' Sithinator by deflecting a shot that was meant for Perry.
Buford found a great robe with one little gash laying around on the Death Star.
The destruction of Alderaan is Played for Laughs twice, as is a Stormtrooper falling out of the Death Star and floating hopelessly in space.
Big "SHUT UP!": Phineas' reaction to Darth Ferb's invitation to join The Dark Side, although it's out of disbelief and amusement at what Phineas thinks is a joke.
The inversion is that she thinks she's a good guy. The girl just wants to be in the frontlines, but her commanding officer won't let her.
Being Evil Sucks: Actually inverted with Candace, but not Baljeet and Buford.