Monsignor Martinez live action pilot (partially found King of the Hill spin-off; 2000)
Monsignor Martinez was a live-action pilot commissioned by Fox in 2000. It was based on the in-universe show of the same name from King of the Hill and starred Ivo Cutzarida in the titular role.
The pilot, titled "In the Beginning", was written by Mike Judge, Greg Daniels (co-creators of King of the Hill), and Jim Dauterive (who served as executive producer and writer for the aforementioned animation), though it was ultimately declined by Fox, who opted out of airing it. The reason they suddenly decided not to greenlight it isn't fully known, though actor David Herman, who voiced John Smith in the pilot and who is known for voicing a number of characters in King of the Hill, suggested that, while he thought it was a very good show, Fox didn't want it due to the fact that a priest was "going around shooting at people" in the pilot.
The pilot is not fully available, although Dauterive claimed that it was posted on Youtube at one point, but was then taken down due to a copyright claim. Additionally, at least one person has claimed to have been sent a VHS screener copy of the episode shortly after it was produced, although the said claim has never been verified and the pilot, as of this writing, remains mostly lost.
In late 2019, a Reddit user called "juanitosay" created a text post on the /r/KingOfTheHill subreddit titled "I HAVE A COPY OF THE MONSIGNOR MARTÍNEZ PILOT!" In the post, juanitosay stated that he had found three copies of the pilot on both VHS and BetaMax formats. He claimed that he wasn't sure about uploading the entire pilot to YouTube, but he intended to put together a documentary for his YouTube channel which would elaborate on the pilot and show much of the footage. His post claimed that the documentary would hopefully be ready in ten days, but no such video surfaced. 
Shortly after, juanitosay returned to /r/KingOfTheHill and uploaded four seconds of footage appearing to show Ivo Cutzarida as Monsignor Martinez during the climax of an action scene at an airport. Martinez, behind the wheel of an airport vehicle, says "Vaya con Dios" as another character is sucked into the turbines of a jet engine.
In 2020, juanitosay returned to the comment sections of his previous posts and responded to questions regarding the status of the project. He stated that the documentary is still underway, but nearing completion, with the intent of recording an interview with Ivo Cutzarida.
Separately, in March 2020 the website Cinedump hosted an editorial written by Jessie Hobson saying that Joe Climan, a member of the media collector's group VHS Misfits, had received a VHS copy of the pilot from producer Stu Segall. The tape supposedly features a rough cut of the pilot with no music and a substandard audio mix. Climan has been screening the pilot at his home and is allegedly trying to contact Mike Judge to proceed with sharing the video legally. 
- IMDb thread from July 18th, 2010, in which a user claims to have seen the episode via a screener VHS tape. Archived 11 Feb '17.
- IMDb page on Monsignor Martinez. Retrieved 11 Feb '15.
- The King of the Hill Fansite trivia page. Retrieved 11 Feb '15.
- I HAVE A COPY OF THE MONSIGNOR MARTINEZ PILOT Retrieved 13 Apr '20.
- First footage ever released from Monsignor Martinez Pilot! Retrieved 13 Apr '20.
- EXCLUSIVE: Monsignor Martinez Pilot Found! Retrieved 22 Apr '20.