"Mecha-Streisand" is the twelfth and penultimate episode of the first season of the American animated television series South Park. It originally aired on Comedy Central in the United States on February 18, 1998. In the episode, Barbra Streisand obtains the Diamond of Pantheos from Stan, Cartman, Kyle and Kenny, and transforms into a giant mechanical dinosaur called Mecha-Streisand. She is ultimately defeated by The Cure frontman Robert Smith, who himself transforms into a giant moth monster.

The episode was written by series co-creators Trey Parker and Matt Stone along with writer Philip Stark, and was directed by Parker. "Mecha-Streisand" parodies numerous popular Kaiju films and features portrayals of actor Sidney Poitier and film critic Leonard Maltin.

According to Nielsen ratings, "Mecha-Streisand" was watched by 5.4 million viewers, a record high viewership for a South Park episode at the time. Streisand herself was critical of the series and her role in "Mecha-Streisand", although Leonard Maltin was complimentary about his portrayal.

During a field trip to an archeological dig, Eric Cartman discovers a mysterious stone triangle, which he promptly throws away without interest. Shortly after Kyle Broflovski picks it up, the guide identifies the writing on the triangle as Anasazi. Kyle appears on television to discuss the find, resulting in a jealous Cartman's wanting the triangle back. Cartman constantly pesters Kyle until he returns the triangle to him. Meanwhile, Leonard Maltin comes to South Park and asks Chef whether he has seen Barbra Streisand. Maltin, having seen Kyle and the triangle on television, tells Chef the boys are in great danger.

Streisand herself finds the boys at the bus stop and demands the "Triangle of Zinthar", and gets angry when they reject her. As they search for Streisand, Maltin tells Chef she is seeking the boys' triangle to complete a powerful and ancient relic, the "Diamond of Pantheos", which will allow her to become an evil and dangerous creature capable of conquering the world. He explains that the diamond was originally split into two pieces and hidden at different points of the world, but Streisand had managed to find the first of the two. Streisand later dons a disguise and visits the boys again, offering them a monetary reward for the triangle. Stan Marsh, Kenny McCormick and Kyle are suspicious, but Cartman insists they go along for the money.

Streisand takes them to her condo in the mountains, where she chains the boys up and tortures them with her singing voice. Cartman relents and gives up the triangle. Streisand uses the triangle to complete the diamond, transforming herself into a giant mechanical dinosaur version of herself, Mecha-Streisand, and begins to lay waste to South Park (and the Colorado National Guard that was sent in to fight her) with her new form. Maltin and Chef arrive to free the boys, and Maltin asks Chef to call Robert Smith of The Cure for help. Maltin then transforms into a giant robot to battle Mecha-Streisand, but is quickly defeated. The boys evade fiery debris from the fight, but Kenny is killed when he stops to play tetherball and gets strangled by the rope. Actor Sidney Poitier arrives and turns into a giant fanged turtle to fight Mecha-Streisand, but he too is easily defeated. After getting a call from the boys and Chef, Robert Smith arrives and transforms into a giant moth creature.

During the ensuing battle, Smith-Moth manages to punch the Diamond of Pantheos away from Mecha-Streisand before flinging her into outer space, where she explodes and dies. The townspeople, including Jesus, joyfully praise Smith as a hero. As the singer walks off into the sunset, Kyle calls out "Disintegration is the best album ever!". The boys split the diamond again to try to prevent anyone else from getting its power and throw the pieces in the trash can. However, Kyle's little brother Ike finds the pieces of the diamond in the trash, resulting in the episode ending with the boys cowering in the presence of a new foe: Mecha-Ike.

"Mecha-Streisand" was written by series co-creators Trey Parker and Matt Stone, along with writer Philip Stark, and was directed by Parker. "Mecha-Streisand" first aired on Comedy Central in the United States on February 18, 1998. Robert Smith, lead vocalist and guitarist for the English rock band The Cure, makes a guest appearance as himself, marking only the second time a celebrity guest played a major role in an episode, after Natasha Henstridge in "Tom's Rhinoplasty". Following the success of "Mr. Hankey, the Christmas Poo", a large number of celebrities started contacting Comedy Central with the hopes of making guest appearances in South Park episodes, allowing Parker and Stone to practically take their pick of guest stars. Parker, a fan of The Cure, said it was his lifelong dream to meet Smith, and he was one of the few celebrities Parker specifically requested to make an appearance. Smith performed all of his lines via telephone and Parker used the first reading of each line, even though they were executed in a very dead-pan voice.