Have you heard of the Teenage Mutant Ninja Turtles comics that appeared a few years before the animated series (1987-1996) this were mature content that has bloody or brutal violence came out in 1984 originally in black & white but later in color and had some panels in the 1990 live-action movie.

Of course! The turtles met them in their multiverse episode, too. Which came out yearsss before any other multiverse show or movie.