The flute solos played by the Pied Piper we're played by [?] Jeremy Steig, a well-known jazz flutist. He is also the son of William SteigWilliam Steig, the author of the original [Shrek] books.
This is not Pied Piper's first appearance. He also appears briefly in Shrek. He can be seen when Shrek first finds all the fairy tale creatures in his swamp, fluting dozens of rats. He looks very different and is wearing red clothing instead of black.
As the head of story, Walt DohrnWalt Dohrn would perform all the voices during storyboard meetings. No other actors came close to matching the voice he had come up with for Rumpelstiltskin and so he was cast.
Rumpelstiltskin appears briefly in Shrek the Third, but looks very different there (wide-brimmed hat, trimmed beard, mustache and sideburns, different facial features) and is voiced by a different actor.
At the very beginning of the movie, the sign for the trailer park where Rumpelstiltskin lives has the inscription "Abandon all hope ye who enter here", which is what is said to be on the gates of Hell, according to the English translation of [?] Dante Alighieri's The Divine Comedy.
One of Rumpelstiltskin's witch cronies is named "Baba", after the witch from Slavic/Russian folklore Baba Yaga.