Rick and Morty didn't miss a chance to take a shot Zack Snyder's Justice League in its second episode of Season 6. Rick and Morty Season 5 had to go into production before The Snyder Cut of Justice League finally got its big release on HBO Max in March of 2021, so the makers of the show have had to wait their fair share of time before getting this joke in. And they definitely make it worth it, by forcing us to do some serious DC Movie math!
In "Rick: A Mort Well Lived" we pay a revisit to the famous "Roy: A Life Well Lived" game at the intergalactic Blips and Chitz arcade – only this time they visit on a wrong day, indeed. A group of alien terrorists pulls a Die Hard on Blips and Chitz, and a power outage leaves Morty's consciousness splintered across all the NPCs in the Roy game. Rick has to become Roy in order to save Morty's mind – which basically requires him to convince a digital world of billions of people to all become one again. Naturally, that requires some pretty deep conversations about the nature of reality.
As things come down to the wire, Rick-Roy tells the remaining Morty NPC leader that he's willing to leave the 8% of Morty holdouts in the game forever. According to Rick's logic, Zack Snyder's Justice League is proof enough that missing 8% of something isn't all that bad, because, "8% of the Snyder Cut was Batman dreaming."
Zack Snyder's epic superhero team-up film runs an equally epic four hours in length. The last fifteen minutes of the movie is a sequence that looks in on the dystopian future of the DC Films Universe after Earth has been conquered by Darkseid and the forces of Apokolips. The sequence ends with the reveal that it is just a precognitive dream Bruce Wayne is having – the second such vision after the first look into the future Bruce saw in Batman v Superman. These sequences have become infamous, as they clearly are building up a complex time-travel storyline that Zack Snyder never got to finish in his planned Justice League sequels. So now, as Rick jokes, it's just extraneous material that hangs out there feeling wholly out of place in Snyder's movies.
By the way: 15 minutes out of 242 minutes is closer to 6%. It goes up if you're talking about the entire Epilogue section of Zack Snyder's Justice League, but not all of that is Batman's dream. Just to be clear.
Rick and Morty and Zack Snyder's Justice League both stream on HBO Max.