Typical traits in Mozart’s variation works are: variations that become progressively difficult, one variation in the minor mode, an Adagio tempo for the penultimate variation and a change in meter in the last.
Even the first two surviving sets, K. 24 & K. 25, composed when Mozart was ten years old, show some of these traits.
The best known of Mozart’s variations were written in the years after he had relocated permanently to Vienna. In K. 265, on Ah vous dirai-je, Maman, the degree of virtuosity rises to a new level.
There was a time when Mozart’s variation works were among the most popular items in the repertoire.
Nowadays, one rarely hears anything but the one just mentioned and perhaps also the Variations on Unser dummer Pöbel meint, K. 455, a really fine work where Mozart uses Gluck’s simple tune to show his mastery of melodic, harmonic and contrapuntal elements.