Which episode of "Rick and Morty"  aired unannounced on April 1, 2017 and was replayed every half hour from 8pm to 12am ET, as part of Adult Swim's annual April Fools' prank?
The Rickshank Rickdemption: "The Rickshank Rickdemption" is the first episode in the third season of the American animated television sitcom "Rick and Morty", and the twenty-second episode overall in the series. Rick and Morty (season 3):  It premiered with "The Rickshank Rickdemption," which aired unannounced on April 1, 2017 and was replayed every half hour from 8pm to 12am ET, as part of Adult Swim's annual April Fools' prank.
"The Rickshank Rickdemption"