When people pick up the first appearance of Deadpool, New Mutants #98, sometimes they forget two other characters got introduced at the same time. They were Gideon and Domino. Gideon never quite caught on, but Domino did, and now it seems she may be showing up alongside Wade in Deadpool 2. Minor spoilers follow.
Heroic Hollywood is reporting that Domino will join Deadpool and Cable (revealed by DP himself in the film's end credits) in the sequel, which is currently being written by Paul Wernick and Rhett Reese. This makes sense for a bunch of reasons.
When comic readers first met Domino, she wasn't actually Domino at all. She was a character named Copycat, a shape-shifter who had captured the real Domino and was posing as her. Here's the kicker: In the comics, Copycat was actually Vanessa, Deadpool's girlfriend, played by Morena Baccarin in the movie. The real Domino is a woman named Neena Thurman who was experimented on and given the ability to manipulate luck, which comes in handy when you're a gun-toting assassin.
So will Morena Baccarin's Vanessa gain shapeshifting powers? And if so, will she masquerade as Domino? We don't know. We just know it's likely she'll be in the movie, and she'll make a worthy adversary (and eventually ally) for Deadpool and Cable if this is all building to an X-Force movie.