Has an AFL game ever ended 77-42?
Exactly once. On June 22, 1929, Carlton beat Melbourne 77-42, and no AFL game before or since has ended that way. When it happened it was a scorigami, the first 77-42 in league history.
That makes 77-42 the 3836th most common final score out of 6,607 that have ever occurred in AFL. One point away, 78-42 has happened 4 times and 77-43 has happened 2 times.