I wonder what it was like to be a designer on one of these Japanese monster shows. You could (at least sometimes, one would imagine) work you ass off to design a really cool monster, knowing in advance that by far the most likely outcome is that the monster will never appear in anything ever again. Maybe the designers wrote each monster a haiku expressing the ephemeral quality of their existence.
In a best case scenario, you get something like Ultraman, that lives on from iteration through iteration, allowing for monsters to be reused occasionally, and even get radical new re-designs that at least pay homage to the past.
Still…the first episode of Japanese Spider-Man, for instance, features this really loveable Gorn-like monster. Five minutes onscreen, and poof, he’s gone. I mourn you, Gorn-like Japanese Spider-Man monster.