Johann Mederitsch – Wikipedia composed the 1st Act.
Johann Georg Anton Mederitsch, called Gallus-Mederitsch (baptised 27. Dezember 1752 in Wien; † 18. Dezember 1835 in Lemberg), was an Austrian composer, conductor and teacher.

Peter von Winter composed the 2nd Act

The intention to follow-up to the succes of Magic Flute with an effectful title was surely a pure motive of Schikaneder.

There have been attempts to follow the success of Magic Flute without direct relation to the story: Die Waldmänner (1793, Henneberg), Der Höllenberg (1795, Wölfl), Der Spiegel von Arkadien (1794, Süßmayr).

A real sequel was tried by Goethe but composed and performed 100 years later in 1891 with “Sarastro” after enlarging Goethe´s fragment to a libretto by Gottfried Stommel.

For the celebration of 100. year after Mozart´s death the Liszt student Karl Eduard Goepfart performed this sequel in Hengelo/NL.

So Schikaneder recognized this potential of good sequels and engaged Johann Mederitsch to compose Act 1 and Peter von Winter for Act 2, finally the performed it already in 1797: Die Pyramiden von Babylon.

First performance 25. Oktober 1797 Freihaustheater auf der Wieden Wien.

Aufführungen im Ständetheater von Prag 1815-06-23 und 1815-06-27

https://lccn.loc.gov/2010661002

libretto Hamburg : Gedruckt bey Johann Gottfried Müller, 1807.

IMSLP vocal scores and libretto (DE)

Sarastro ist the title of the opera (originally called: „Musikdrama“) of Karl Goepfart, which is a sequel of Zauberflöte of Wolfgang Amadeus Mozart and Emanuel Schikaneder. The Libretto by Gottfried Stommel is based on the fragment of Johann Wolfgang von Goethe “Der Zauberflöte zweyter Thel” and develops into an own story. The World premiere was 9th December 1891 concertante in Hengelo/NL..

Sarastro (Oper) – Wikipedia (DE)

Das Labyrinth oder Der Kampf mit den Elementen. Der Zauberflöte zweyter Theil (“The Labyrinth or The Struggle with the Elements. The Magic Flute’s Second Part”) is a “grand heroic-comic opera” in two acts^[1] composed in 1798 by Peter von Winter to a German libretto by Emanuel Schikaneder. The work is in the form of a Singspiel, a popular form that included both singing and spoken dialogue. The opera is a sequel of Mozart‘s The Magic Flute.

Das Labyrinth – Wikipedia EN

The Magic Flute (German: Die Zauberflöte, pronounced [diː ˈtsaʊbɐˌfløːtə] ^ⓘ), K. 620, is an opera in two acts by Wolfgang Amadeus Mozart to a German libretto by Emanuel Schikaneder. The work is in the form of a Singspiel, a popular form during the time it was written that included both singing and spoken dialogue.^[a] The work premiered on 30 September 1791 at Schikaneder’s theatre, the Freihaus-Theater auf der Wieden in Vienna, just two months before the composer’s premature death. It was the last opera that Mozart composed. Still a staple of the opera repertory, its popularity was reflected by two immediate sequels, Peter Winter‘s Das Labyrinth oder Der Kampf mit den Elementen. Der Zauberflöte zweyter Theil (1798) and a fragmentary libretto by Johann Wolfgang von Goethe titled The Magic Flute Part Two.

The allegorical plot was influenced by Schikaneder and Mozart’s interest in Freemasonry and concerns the initiation of Prince Tamino. Enlisted by the Queen of the Night to rescue her daughter Pamina from the high priest Sarastro, Tamino comes to admire the high ideals of Sarastro. He and Pamina both join Sarastro’s community, while the Queen and her allies are vanquished.

Der Stein der Weisen, oder die Zauberinsel (German for The Philosopher’s Stone, or the Enchanted Isle) is a two-act singspiel jointly composed by Johann Baptist Henneberg, Benedikt Schack, Franz Xaver Gerl, Emanuel Schikaneder, and Wolfgang Amadeus Mozart in 1790. The libretto was written by Schikaneder.

Der Stein der Weisen was composed using a “team approach” in which each composer contributed individual sections of the piece. All five wrote parts of act 2, and all except Mozart wrote parts of act 1. Henneberg composed the work’s overture. Schikaneder wrote the libretto for the entire piece. The text is based on a fairy tale from Christoph Martin Wieland‘s Dschinnistan [de], published in the late 1780s.

All five were later involved in The Magic Flute: Mozart as composer, Schikaneder as librettist, impresario and performer (Papageno), Henneberg as conductor, and Schack and Gerl as performers (respectively Tamino and Sarastro). Der Stein der Weisen may have provided a model for that work, as the two have a similar structure and source.

The work was initially popular, but was largely absent from the standard repertoire for the two centuries after 1814. American musicologist David Buch announced the discovery of a Viennese score with attributions to all five composers.^[5] This was taken by some to indicate that Der Stein der Weisen was a previously unknown Mozart work, although in fact only a duet (“Nun, liebes Weibchen”,^[6] known as the “cat duet”) and two sections of the act 2 finale were attributed to him.^[2]

The autograph of “Nun, liebes Weibchen” (K. 625/592a) is held by the Bibliothèque Nationale in Paris; the rest of the original score is lost. The work is known from a ca. 1795 copy.

The singspiel was premiered on 11 September 1790 in the Theater auf der Wieden, conducted by Henneberg. It was first recorded by the Boston Baroque in 1999. Modern performances were mounted at the Hampstead & Highgate Festival, Augsburg Opera and Pepperdine University in 2001, by Bampton Classical Opera in 2002, by Combattimento Consort Amsterdam in 2003, the Astoria Music Festival, Garsington Opera and Salzburg’s Haus für Mozart in 2006, Opernhaus Zürich (at the Stadttheater Winterthur) in 2010, and the Tiroler Landestheater in Innsbruck in 2018.