At point when the kids are on ride that Phineas and Ferb have built, they are shown with the heads of the voice actors for the characters.
Candace asks Phineas, "you, boy, what day is this," which is reference to Charles Dickens' novel "A Christmas Carol."
The last episode of the series.
This episode is based on Groundhog Day.
Multiple scenes in "When Tomorrow is This Morning Again" are a call-back to "Busted", with Doofenshmirtz in Vanessa's positions.