The third BLADE film, BLADE TRINITY, is the only one to qualify as a crossover. It includes a version of the Marvel hero Hannibal King, albeit with assorted changes from the original model, and yet another version of Dracula, having nothing to do with either Stoker or the Marvel Comics incarnation.
One episode of the Japanese-made BLADE teleseries sports a crossover with Wolverine.
It's double your Golden Age villainy as the Hangman battles both Captain Swastika and the Executioner! (What, no fiendish representative for Italian fascists?)
Though Mademoiselle Marie lost her series in the early sixties, she kept showing up in other DC features.
Like teaming up with the Hellcats in the early seventies.
And a decade later, with the Unknown Soldier a few times.
Since I ventured into POPEYE criossovers in my last post, I may as well note that I'm aware of one "super-villain team-up" in the sixties POPEYE TV cartoons executed by King Features. In "Private Eye Popeye" (a title already used for one of the Paramount theatrical shorts). Brutus, a creation of the King animators, teams up with The Sea Hag, a product of the comic strip.
They also appear, though not as a team, as participants in a scheme to get Popeye to show up on a "This is Your Life" program in the episode "Strange Things Are Happening."
In my previous post I mentioned that I wasn't sure if Popeye in the comic books ever crossed over with the separate E.C. Segar creation O.G. Wotaschnozzle, a mad professor. But "Strange Things" also uses a scientist by that name, even though he's terribly off-model, not even having his distinguishing oversized schnozzola.
Obviously the crossover of the MARS ATTACKS franchise with that of Popeye is the one-shot's main appeal. Yet there's also a more minor crossover in that one of the E.C. Segar characters shown above was not created for the Popeye universe, even when the strip was still called "THIMBLE THEATER." The bearded fellow with the huge schnozz is Professor Wotaschnozzle, and as the late Don Markstein helpfully noted, Wotaschnozzle first appeared as a support-character in a 1932 sequence of Segar's separate SAPPO comic strip. Much as Popeye took over THIMBLE THEATER from its default "star" Castor Oyl, Wotaschnozzle edged out the titular character John Sappo and dominated that strip until it ended in 1938. Then, as Markstein explains, Segar's successor on POPEYE Bud Sagendorf revived O.G. Wotaschnozzle for a back-up series in POPEYE comic books, though in this incarnation Wotaschnozzle got top billing and Sappo was just support-cast. I have no idea if Wotaschnozzle crossed over with any POPEYE characters during his comic-book years, so it's possible that Powell and Beatty authored the first such interaction in this 2013 project.
I certainly wasn't expecting to find a monster mashup in the pages of a Golden Age SHADOW comic (v. 3, #8), but here's a scene in which a Sphinx outstares a Cockatrice. The bearded fellow summoning three other monsters-- all doomed to get "stoned" by the Sphinx's glare-- is a comic-book foe of the Dark Avenger, name of "Monstrodamus."
In my review of the 1923 novel THE MOON MAID I commented:
I don't know about the other two parts, but MOON MAID is part of a loose continuity with the Mars books. It's through Earth's radio contact with Mars that future-Earth perfects space travel with the use of Martian "rays," and Storytelling Julian even mentions John Carter, though it's not clear just what he knows about the Martian hero.
The book stands as a "null-crossover" in my system because John Carter and his Martian domain are referenced but none of the icons therefrom are present in the story. ERB does name the hero's spaceship "The Barsoom," which was the author's canny way of evoking the Mars books within a technically unrelated story.
ADDENDUM: Barsoom-Mars is also "in-universe" with the sequel novels as well, but the name is only mentioned in passing within the first sequel and not at all in the second.