At the end of "What's Up Duloc," the riff Sieber sings is actually from Defying Gravity, a song in Wicked.
The film Shrek was made to poke fun at the Disney empire. The Broadway incarnation contains the tradition with references to a slew of other musicals, including Wicked, Chicago, The Lion King, Gypsy, Les Miserables, Once Upon a Mattress, RENT, A Chorus Line, Evita, and Dreamgirls.
During the beginning song, "Big Bright Beautiful World," as young Shrek is traveling to his new home, there is a family of royals, leading a young redhead, Princess Fiona, who waves at young Shrek.
In the song "ballad of Farquad" Farquad references that his father is grumpy, one of the seven dwarves", and implying his mother is the princess from The Princess And The Pea.
It took about an hour and a half for Brian d'Arcy James to get into makeup.