Pirates vs. Ninjas vs. Zombies vs. Robots (1936)
. . . Or it could be a mashup I finished last night. Featuring Boris Karloff, Charles Laughton, John Carradine, Randolph Scott, Duane Jones, Fei Meng, Bela Lugosi.
I used clips from the following movies, all public domain as far as I know:
Captain Kidd (1945)
She hao dan xin zhen jiu zhou (1976), a.k.a. Snake Crane Secret
Night of the Living Dead (1968)
Revolt of the Zombies (1936)
La Muerte Viviente (1971), a.k.a. Snake People
La Guerra dei Robot (1978), a.k.a. War of the Robots
The Phantom Creeps (1939)
Voyage to the Prehistoric Planet (19??), lots of varied editions derived from some original Russian film.
These can probably all be found on archive.org.
With music clips from Captain Kidd, Captain Scarface, and The Iron Mask (1929). The Iron Mask was a silent movie starring Douglas Fairbanks Sr., filmed in 1929. It was reissued with a soundtrack, including narration and voiceover by Douglas Fairbanks Jr. in 1952, and that's the theme music used for most of this mashup.