When a TV series is canceled, the act can give the writing staff, actors, and crew permission to throw caution to the wind. They often use the final episode to do things they were too timid to attempt before, or maybe even shoot for the moon by doing something so different they would otherwise be fired over it. We're talking about plots that went way past revealing it was all a dream, which was done for Newhart (which was clever) and for St. Elsewhere (which was not).
Having a weird finale is even weirder when it's not on purpose. Family Matters and ALF made the list even though the final episode was completed before they found out about their cancellation. Revisit how eight different TV series went out with a bang, even when they didn't mean to, at Mental Floss.
Oh yeah, relive those moments with video evidence.