It must be obvious from this site that I am a big fan of Die Zauberflöte. And I really like many of Mozart’s other operas (Le Nozze di Figaro, Die Entführung aus dem Serail to name a couple). But along side these, my “desert island” collection would include lots of Beethoven.
Mozart was a major influence on Beethoven. Beethoven traveled to Vienna during the period Mar.-May, 1787 to study with Mozart (but was called back to Bonn when his mother fell ill). He had great respect for Mozart. In 1796 Beethoven wrote in a letter “I have always counted myself amongst the greatest admirers of Mozart, and shall remain so until my last breath”.
Beethoven wrote a number of variations based on themes from Mozart operas. He considered Die Zauberflöte to be Mozart’s best.
In 1796, Beethoven wrote 12 Variations for Piano & Cello in F major on “Ein Mädchen oder Weibchen”, Op. 66. Here are variations one and two.

In 1801 Beethoven wrote 7 Variations for Piano & Cello in E flat major on the duet “Bei Männern, welche Liebe fühlen”, WoO 46. Here is the first variation.

notes:
These performances are from a recording of Beethoven Cello and Piano music with Pablo Casals and Rudolf Serkin, Sony CD SM2K 58985.
The quote above is taken from The Beethoven Compendium, ISBN 0-500-27871-1

The role of the Königen der Nacht (the Queen of the Night) is the “diva” role in Die Zauberflöte. The role has lots of “virtuoso” singing (coloratura) and she usually gets a big entrance and a  great costume. The Queen only has two arias but a good performance (singing and acting) is really important for the entire opera. Because the Queen of the Night is crazy.
Mozart’s music is brilliant at demonstrating for us that this is so. But we don’t know that right away. The Queen’s first aria starts out rational enough. “Oh, zitt’re nicht, mein lieber Sohn!” (“Don’t quake [before me] my beloved son!”) begin her words to Tamino. And the music portrays her as rational enough. She goes on to explain how her only daughter was kidnapped from her by the evil Sarastro and she was powerless to intervene (“Denn meine Hilfe war zu schwach” (“For I was too weak to help”)). And we really feel her pain. Mozart is really brilliant.
Then, we see her true colors. We can almost feel her crack when the tone of the music shifts as she sings “Du, du, du! wirst sie zu befreien geben. Du wirst der Tochter retter sien.” (“You, you, you! will release her. You will be the saviour of my daughter.”). Now, I am not a big fan of coloratura but the Queen’s next bit can only be Mozart’s way of showing us that she is mad. Did I say that Mozart is brilliant? But poor Tamino. What a wimp. He falls for it all.
When the Queen returns in Act II, the coloratura is over the top. Absolutely brilliant. (That word again. Hard to avoid it when talking about this opera.) Kill Sarastro, she tells Pamina. Do it or you are no longer my daughter. Wow, is that dysfunctional or what? Like I said, the Queen is crazy. And the music that Mozart provided her is just beautiful. Beautifully mad.
Here is the great Erna Berger as the Queen singing the second act aria “Der Hölle Rache kocht in meinem Herzen”(“Hellish revenge roils in my heart”). Pretty strong stuff!
This is from a 1938 recording with the Berlin Philharmonic conducted by Sir Thomas Beecham.