Deadpool's popularity has given rise to any number of zany crossovers and team-ups over the years. Which is, more often than not, totally fine. One might even say that the Merc' with a Mouth is best served by having straight-faced companions off of which to bounce his nonsense. It certainly worked with Cable, a hero with a face so literally and metaphorically straight you'd need a Hulk-level air drop of puppies just to make him stop frowning.
One event that Deadpool sadly missed out on was the seminal, company-wide Marvel crossover Secret Wars. The likely reason for his lack of inclusion being that he didn't exist at the time. Secret Wars launched in 1984, while Deadpool was a child of the early 90s. Somehow, that didn't stop Marvel from going back to include Wade in the be-all-end-all event more than 20 years later. More than that, they made his role a central one in the story that helped redefine Marvel at the time.
Deadpool's Secret Secret Wars was a more recent retelling of the basic events from its namesake. This time, however, a thoroughly modern Deadpool hobnobs with the 80s versions of heroes from the era. He bumps up against Doctor Doom, hooks up with The Wasp, becomes the reason behind the Venom symbiote turning twisted, and gets his wish for a thoroughly handsome and undeniably of-the-decade makeover. Though by the end his contributions to the cosmic battle go completely forgotten. All thanks to The Wasp "wishing" everyone to forget about Wade in order to salve her own, guilty conscience over being superficial.
It's a... bizarre story, even by Deadpool standards. As far as breaking the fourth wall goes, it's also one of the more subtle instances in the character's run. Indeed, everything Wade does technically could have occurred -- though it would mean rewriting one of the biggest moments in Marvel continuity for the sake of a joke. Though oddly enough that seems entirely appropriate for a character that seems to pull everyone and everything into his wacky, gravitational pull.
Ryan Reynolds basically is Deadpool at this point. Oh, sure, cartoon and game fans may put one Nathan Drake's voice under the red, stretchy mask until the end of time. The other $700 million-plus worth of moviegoers out there would likely disagree. And, you know what? That's okay. The Deadpool movie was fantastic not just on the strength of the character and production team, but also an actor who clearly wanted to bring that role to life.
Apparently the team behind Cable & Deadpool (which included Deadpool creator Rob Liefeld on covers) also wanted Reynolds for the role. That was five years before one fourth of Two Guys, A Girl, and a Pizza Place picked up a pair of katanas and an unhealthy sense of humor in X-Men Origins: Wolverine. Though you can all bet the writers and artists weren't expecting what they got in that particular cinematic dumpster fire.
In a sense this isn't really breaking the fourth wall, given Deadpool is referencing something that hadn't happened yet. Unless, of course, his powers of reality awareness transcend not just his universe, but time itself. Which... Well, we're not ready to put anything past Deadpool just yet. One way or another, the message reached Reynolds himself, who claims the aforementioned issue was the first one he ever read.
Eventually, however, Wade got to make good on his cinematic counterpart's painfully awful role. Well, very nearly at least. Five years after Origins (and two years before Reynolds and company made the sad times go away with a proper Deadpool movie) Wade was hanging out with the Thunderbolts. At the time, this was a group of variously powered or un-powered antiheroes with a red color scheme. So, of course, that included Deadpool.
The team took to drawing lots. Whoever's name was pulled out of the hat could count on the resources of Elektra, Ghost Rider, Red Hulk, Venom, Deadpool, and a newly altered version of the Hulk villain, Leader, at their disposal. Once it was Deadpool's turn to choose we got tantalizingly close to learning what revenge he had in store against Reynolds, though he was quickly interrupted.
Now, with the whirlwind romance between Reynolds and Wilson at a high point, it's probably time for another comic to revise that somewhat menacing sentiment.