Examples of DC References in Marvel Comics:
* The Squadron Supreme: This Marvel team is a blatant parody of the Justice League. They even have similar members with similar powers, like Hyperion (Superman), Power Princess (Wonder Woman), and Nighthawk (Batman).
* The Fantastic Four: In the original Fantastic Four #1, the team is shown battling "the Mole Man." This was a reference to the DC character, the Mole Man.
* Spider-Man: In a story from the 90s, Spider-Man is shown reading a comic book that looks suspiciously like "Batman" and referencing the "Batcave."
* Deadpool: Deadpool is known for breaking the fourth wall and referencing other universes, including DC. He's even battled a Batman parody called "Bob, the Batman."
It's important to note that these are just references and not official crossovers. The two companies have very strict intellectual property rights and wouldn't allow their characters to be used in each other's stories.
While it's unlikely to happen, there are some fans who dream of a crossover between Marvel and DC. This would be a massive event, but it's simply not in the cards for now.