Exactly as it says, you can replace the cast of any movie with The Muppets, but you have to keep one of the movie actors.
What movie and which human do you keep?
For example, the Chris Nolan Batman Trilogy with Michael Caine as Alfred as the only human.
Or The Terminator with Arnold Schwarzenegger as the only human (well cyborg) would be pretty entertaining/alarming.
Any ideas? 
Austin Powers, IMoM. Kermit as AP, Miss Piggy as Vanessa, Fozzie as Number Two, Bunsen as Basil Exposition, and Mike Meyers as Doctor Evil. With beaker as Mini-Me. Statler and Waldorf can, as always, supply running commentary.
Does it have to be a recent enough film that the human actor is still available? Because I’d like to see Casablanca with Kermit as Rick and Miss Piggy as Ilsa but keeping Claude Rains as Renault. (Actually, they may have done a parody of Casablanca on their variety show.)
The Empire Strikes Back, with Frank Oz as Yoda.
Robin Hood: Prince of Thieves.
Keep Alan Rickman as the Sheriff of Nottingham.
The “True Detective,” where Marty is Woody Harrelson and everyone else - including Rust - is a Muppet.
Harrelson: “So what’s the point of getting out of bed in the morning?”
Muppet: “I lack the constitution to commit suicide.”
That would actually be a fantastic movie.
Nope, any era is fine 
The original* The Producers*, with Kermit as Leo, Fozzie as Max. Gonzo as Roger DeBris, and the Swedish Chef as Franz Liebkind. Keep Dick Shawn as Lorenzo St. Dubois.
Muppet Lord of the Rings — keep Sir Ian McKellen as Gandalf.
Right actor, wrong movie. Redo Sleuth with Caine as Andrew Wyke and Kermit as Milo Tindle.
Sleuth has been a movie twice, originally with Caine as the younger Milo, and the remake had him as the older Andrew. For my version, I would keep the style of the original, but with Caine in the senior role as in the remake.
Jaws. Keep Robert Shaw.
The Godfather, with Kermit as Tom Hagen, Miss Piggy as Kay, Beaker as Don Vito, Sam the Eagle as Sonny, Gonzo as Fredo, Fozzie as Clemenza. Keep Pacino.
Pulp Fiction, because I now can’t stop picturing Fozzie shooting Marvin in the face and Kermit’s reaction: I figure Sam The Eagle can do Christopher Walken’s part, and I figure Miss Piggy for Uma Thurman, and figure Gonzo delivers every Bruce Willis line (only to, y’know, a chicken as his love interest), and figure Dr. Teeth and Janice swap in as Ringo and Honey Bunny, and so on; but the key is, the guy who doesn’t even have an opinion and gets killed by a muppet who wasn’t even trying — and nobody really much cares, except that he now mildly inconveniences other muppets?
Yeah, he’s the human.
(Rowlf as Ving Rhames and the Swedish Chef as Harvey Keitel, or vice versa?)
Peter Jackson’s, “King Kong,” with Jack Black as Denham, Piggy as Naomi Watts, Kermit as Adrian Brody and Fozzie as Andy Serkis.
No. The one cast member you keep is S.Z. Sakall, who looks like a Muppet to begin with. Rowlf as Sam, Sam the Eagle as Major Strasser, Rizzo the Rat as Ugarte, Fozzie as Laslo, Dr. Teeth as Renaukt
12 Angry Men.
Statler and Waldorf as the two antagonists who don’t change their votes until late. Fozzie Bear as the ad exec who changes his vote several times, except in this version he changes it every few minutes in an attempt to gain the validation of his peers.
Swedish Chef or Beaker as the naturalized citizen. Sam the Eagle as the foreman.
As for the human, that would logically be Henry Fonda, but I could also see a case being made for Joseph Sweeny instead (the old dude who changed his vote and stood up for Fonda). Kermit the Frog would play whichever of those is not a muppet.
Aso, humans (yes, plural, I know I’m cheating) could be the various minor roles like bailiff and judge, and in the spirit of other Muppet movies they would all be improbably high-profile cameos.
I was thinking keep Abe Vigoda, but he’d have to be written in to a lot more scenes.
Guy Smiley as Lazlo, Uncle Deadly as Major Stasser, Sam the Eagle as Ferrara, Wayne and Wanda as the couple whom Rick helps at the roulette wheel. Floyd as the owner of the second-largest bank in Brussels, and Janice as his wife. I would keep Peter Lorre.
I was going to mention Requiem for a Dream, but it’s too awful to consider.
How about Fight Club with Brad Pitt staying as Tyler Durden? The plot twist would be even more surprising.
I think we need a Muppet horror movie. How about The Shining?