The trailer shows several glimpses of weird and exciting elements of the new season, but none are more significant than the return of Mr. Meeseeks. The fifth episode of S1 entitled "Meeseeks and Destroy" featured the Meeseeks, a race of singular-purposed beings that can be summoned on a whim from a Meeseeks box and stop existing after they complete their purpose. The Meeseeks become violent and desperate after Jerry gives them a purpose that can't easily be fulfilled: taking strokes off of his golf game. Fans of the show will surely be interested to see what existential crisis Mr. Meeseeks faces this time around.
The November release for Rick and Morty S4 was announced by Adult Swim back in May (see "'Rick and Morty' Season 4").