One of the few piano compositions written by Mozart during his time in Vienna is the Allegra KY 400, probably composed as the first movement of an entire sonata. Even this allegro has been handed down in fragments only: Mozart only wrote the exposition and development sections. We have to thank the rules of the sonata form for stipulating a certain similarity of exposition and reprise, so that Abbé Stadler succeded in completing this movement in a faithful manner. Transcribing Mozart's music for two flutes is by no means an invention of our days. There are numerous contemporary arrangements, e.g. of opera arias and violin sonatas, perhaps they were written by Mozart himself.
Difficulty level, roughly compared to ABRSM exam grades. 0 is beginner, 9 is advanced (beyond grade 8).