I happened on a query where, by mistake, an
SELECT ... ORDER BY x DESC LIMIT 1
was written as
SELECT ... GROUP BY x DESC LIMIT 1
And it took me by surprise to realize GROUP BY x DESC is a valid statement. I looked it up: yep! It's documented.
In MySQL, GROUP BY results are sorted according to the group statement. You can override this by adding ORDER BY NULL (see past post). I wasn't aware you can actually control the sort order.