The Last of the Wild Horses is not one of the funnier MST3K installments, but it's an interesting one. I watched it last weekend for the first time and ended up really enjoying the host segments. In the Invention Exchange, Dr. Forrester and TV's Frank try to send up their Matter-Transference Device to the Satellite of Love, but they encounter interference from an ion storm. As a result, Tom Servo and Gypsy get transported into an alternate universe where Mike and The 'Bots are the evil scientists running movie experiments on Dr. F and TV's Frank. This leads to Dr. F and Frank actually being in the theater riffing movies and lots of host segments that ape the classic Star Trek episode "Mirror, Mirror".
Unfortunately, I can't find any YouTube clips (though the whole movie is available here), but I did find some as part of a "best of" compilation.
"Great big backs of the Old West."
"Let the Cher jokes begin!"
"Boss, you've broken the Goofy Meter again."