(at around 23 mins) The footage of the X-Men closing the door was shot on the set of X-Men: Dark Phoenix (2019) and sent over to the Deadpool 2 crew.
(at around 1h 4 mins) When Deadpool complains about Domino's powers, he says that it must have been the idea of an artist "who can't even draw feet." Domino and Deadpool's co-creator Rob Liefeld is widely mocked and criticized for avoiding drawing characters' feet and hands. (He also reportedly loved that joke.)
Brad Pitt admitted that his small appearance satisfied his curiosities when it came to the world of superhero cinema. "I think I've taken it as far as I can take it," Pitt revealed to MTV News about the role. "Ryan Reynolds came up with a part that I could fill."
Ryan Reynolds wrote Brad Pitt a letter pitching the idea of a cameo to him. "I just wrote him a letter, and explained what it was we were doing," Reynolds said. "And the sort of premise behind it was how do we, what's the most wasteful way to use the biggest movie star in the world? And it was through a character that is largely invisible and worthless throughout the movie." He continued, saying Pitt seemed to like the idea. "And I guess Brad found that funny, we all found that funny. And he said, yes. And the next thing you know he came and shot for about seven minutes," Reynolds added. According to screenwriter Paul Wernick, Pitt jumped at the chance to appear in Deadpool 2: "He immediately said yes," Wernick told Heat Vision per The Hollywood Reporter. "It was a pinch-me moment." Reynolds only had good things to say about Pitt: "He's just such a gentleman, and such a funny, charming human being. And parenthetical the biggest movie star on earth. And that was pretty exciting for all of us."
Ryan Reynolds was at a dinner party with Matt Damon, pitched him the toilet paper manifesto, and asked Damon if he wanted to play the part. Damon thought it was hilarious and agreed to the cameo.
Matt Damon, Alan Tudyk: Two rednecks whose truck Cable steals. Damon, who is unrecognizable under heavy prosthetic makeup, is not credited under his own name but as "Dickie Greenleaf," the name of Jude Law's character in The Talented Mr. Ripley (1999), who is murdered and then impersonated by Damon's character Tom Ripley.