In the late early 1990s, I saw a few minutes of a 1970s/1980s Ninja Movie (not a cartoon or anime, a live action film) on a cheap local UHF TV station.
The movie in question has the following elements:
Had a late 70's, early 80's Ninja Movie feel, both dialogue and plot badly dubbed over the original Asian content
The most striking feature was the bad guys had a flying fortress, a castle build on some kind of floating mountain - you would think this would be a dead giveaway, but a recent Anime claims the first 500 search results for related terms.
When each major character was introduced, the scene would pause with a freeze frame of that person in action, with the background colored out and that persons name printed on the screen. I distinctly remember the narrator saying "...THE KOREAN NINJA...(name forgotten)" for one of the characters.
The Korean Ninja wore wooden sandals, that resembled a rectangular block of wood, with two smaller rectangular pieces of wood affixed to the bottom as a sole.