(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.
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."
(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.)
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.
(at around 1h 8 mins) The gag where Deadpool stops Cable's bullet with a sword and then uses both to "stop" multiple bullets only to realize many of them made it through to his body was conceived by the stunt team. David Leitch passed on it initially as being too comedic for a dramatic sequence, but when he showed it to Ryan Reynolds the actor found it hilarious.
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.