It’s The X-Men!
The first Deadpool featured a great joke in which Wade Wilson visits the X-Mansion and only encounters Colossus and Negasonic Teenage Warhead. “Why is it only always the two of you? It’s like the studio can’t afford anyone else?” he says. In Deadpool 2, that joke’s turned on its head – resulting in a blink-and-you’ll-miss-it cameo from some actual, bonafide X-Men.
Once again, Deadpool visits his old allies at Professor X’s house and complains that there aren’t any other familiar X-Men characters around. As he says this, a door opens behind him, revealing Beast (Nicholas Hoult), Cyclops (Tye Sheridan), Quicksilver (Even Peters) and Xavier (James McAvoy) for a split second before the door’s closed again. It’s a brilliant moment – presumably made possible thanks to Dark Phoenix being in production at the same time as this film.
While in the mansion, Deadpool also can’t resist some more jokes at the Prof’s expense. He drives around in his wheelchair for a while and dons the Cerebro headpiece, breaking continuity by using it to see into the future and mentioning that it “smells like Patrick Stewart.”