Movies within movies.

[Svengoolie 3]

Name a movie where a movie plays a major role in it.

"Lobster man from mars" is a movie based on a crooked producer needing to make a bomb movie as a tax writeoff to avoid prison for embezzlement. An aspiring little Spielberg comes along with his no budget scifi flick "Lobster man from mars" and his prayers seem to have been answered.

[Pacman000]

Singing in the Rain

Hail, Ceasar!

King Kong (Original & Jackson's)

The Reluctant Dragon (Featue-length version)

Sunset Blvd.

Sherlock Jr.

The Cameraman

[RCMerchant]

.SPIRIT OF THE BEEHIVE (1973)- FRANKENSTEIN (1931)
.FADE TO BLACK- DRACULA, PUBLIC ENEMY, the MUMMY, and Marilyn Monroe films.

. RETURN OF THE LIVING DEAD -NIGHT OF THE LIVING DEAD (1968)!

"Burt Wilson: I thought you said if we destroyed the brain, it'd die!

Frank: It worked in the movie!

Burt Wilson: Well, it ain't working now, Frank!

Freddy: You mean the movie lied?"

EDIT: Well, dam. You mean they're filming a movie within a movie?
.the STUNT MAN (1980)
.MATINEE (1993)
.ED WOOD (1994)
.OF GODS AND MONSTERS (1998)
.HOW TO MAKE A MONSTER (1958)

[zombie no.one]

TROPIC THUNDER

[RCMerchant]

.The DEATH KISS (1932) with Bela Lugosi. Awful movie. Even Bela can't save this turd.
.CHAMPAGNE FOR CAESAR (1950) involves not a movie but a TV quiz show. And Vincent Price is in it! Bacon! 

[Alex]

The Dead Hate The Living. A low budget zombie film about the making of an even lower budget zombie film.

[FatFreddysCat]

The 1991 horror film "Popcorn" takes place in an old movie theater, during a marathon of schlocky, William Castle style "gimmick" B&W horror movies ("Mosquito!", "The Stench" and "Attack of the Electrified Man") from the '50s.

[RCMerchant]

.The GREAT WALDO PEPPER (1975)-fun movie!
.LAST HOUSE ON DEAD END STREET (1977) -Not so fun movie!

[The Burgomaster]

* THE FIRST NUDIE MUSICAL (1976)
* THE MYSTERY IN DRACULA'S CASTLE (1973)
* BOWFINGER (1999)

[frank]

Shadow of the Vampire (2000)
Zack and Miri Make a Porno (2008)

[Allhallowsday]

KISS OF THE SPIDER WOMAN (1985)

[claws]

The Disaster Artist (2017)
Argo (2012)
Super 8 (2011)
The Ring (2002)
Cannibal Holocaust (1980)
Last Action Hero (1993)
Orgazmo (1997)
My Week with Marilyn (2011)
The Final Girls (2015)
Barton Fink (1991)
The Artist (2011)
¡Three Amigos! (1986)
Demons (1985)
Matinee (1993)
The Purple Rose of Cairo (1985)
Anguish (1987)

[Pacman000]

The Last Chance - Saw this on TV a few years ago. Probably only funny if you're in the film business. https://m.imdb.com/title/tt0357054/

The Wizard of Speed & Time - Actually pretty good, tho the middle needs work.