Battle of the Planets - Episode 13 - "Perilous Pleasure Cruise"
Ocean liners are being sunk by mysterious forces...
Super President (1967)
3 episodes of the 60s animated series in which the US President is also a shape-shifting superhero on the side
Galaxy Trio - Ep9 "Computron Lives", Ep7 "Titan, the Titanium Man" & Ep12 "Demon Raiders" (Hanna/Barbera, 1967)
Computron's ray gun turns people into robots, and...(spoiler alert) robots into people! Also, Titan, the Titanium Man and Demon Raiders!
Gatchaman - Episode 105 "Earth Extinction 0002"
Eerie stone statues appear in the fog. The Science Ninja Team walks around, searching for the entrance.
Collection: (Sort of) Superheroes
Some of these are "real" and some of these are parodies, but none of them are very helpful.