The only payment Tiffany Haddish asked for for recording her part was a Perry the Platypus T-shirt. Since Disney no longer made those, Dan Povenmire and Jeff 'Swampy' Marsh personally hand-painted one for her.
Most of the original cast reprise their roles, with the exception of Thomas Brodie-Sangster as Ferb, due to schedule conflicts. Instead, David Errigo Jr., who played the role in the Milo Murphy's Law (2016) crossover, voiced the character.
Co-Creator Dan Povenmire confirmed on Twitter that the events of the movie take place before the final episode of Phineas and Ferb (Season 4, Episode 30 "Last Day of Summer"). He was quoted as saying it is set in "Middle of the Summer. Like a lost episode."
With 17 lines (9 of them standalone, and the rest speaking with someone else), this is the most dialogue Ferb has ever spoken. This beats the record of both Phineas and Ferb: Summer Belongs to You! (2010) (9 lines) and Phineas and Ferb: Star Wars (2014) (11 lines).
When Candace tells the Alien spaceship to stop stop stop launching all of the escape pods the computer asks if she wants to hear "Chop Chop Chop" by the Lumber-Zachs. This is a reference to Milo Murphy's Law a show from Disney which was also created by Phineas and Ferb creators Dan Povenmire and Jeff "Swampy" Marsh