The melody that Lisa's crystal is playing is "Drunt im Tal, ja da sitzt das kleine Ottili", a song that Otto Waalkes wrote for his comedy routine when he started his career in the early 70s. He used it in various of his own comedy movies and TV shows.
In 2007 a German production company (possibly the same one behind this film) attempted to make a major film of this story in the UK. The project fell through but in 2011 the project was back on again with Welsh actor Rhys Ifans attached to play the titular medieval magician with filming slated to commence at Shepperton studios. Again, that fell through for some reason and after creator Richard Carpenter died in 2012 it looked like the project was permanently canceled. However this German made film crept out in some European countries in the summer of 2021, although it was never given a theatrical release in Britain or any of the English speaking countries so many fans of the original TV series will not be aware of it.