Known as the 'Good Night' canon, this light-hearted piece by Mozart captures his quintessential wit. It is musically distinguished by its deceptive simplicity and clever harmonic turns.
Practice voicing the melody clearly against the supporting parts.
Bona nox, bist a rechta Ox (K.561) is rated Henle level 2 of 9 — beginner repertoire, roughly ABRSM grades 2–3. In the RCM system it corresponds to about level 3.
You should be comfortable at Henle level 2 — meaning you can already play level 1–2 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Bona nox, bist a rechta Ox (K.561) lasts about 1 minute.
Bona nox, bist a rechta Ox (K.561) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.