Vanessa infiltrated Cable's team, X-Force at it's start posing as Domino and joining the team by throwing kunai knives into Deadpool's back while saying to Cable "You called, I came." Copycat also had a sexual relationship with Cable during this time (unclear if Deadpool is aware). It was later discovered by Cable that Tolliver, Deadpool, and Copycat had been holding the real Domino captive, after freeing her he asked Domino to look after X-Force, but she only gave them Cable's message, and chose to strike out on her own. Copycat never assumed Domino's identity again.
Deadpool: Vanessa loves Wade Wilson to the point of obsession, on the rare times he has not returned her affection she posed as a woman he was dating, sometimes it was revealed Deadpool was never actually dating a woman, but rather Copycat posing as her. She has notably posed as X-Force members Siryn and Domino.
Cable: Copycat posed as Domino during the founding of X-Force, it has been made clear she and Cable had a sexual relationship during X-Force's beginning. It is also indicated that much of Cable and Domino's romantic relationship actually took place between Cable and Copycat.
Garrison Kane: Copycat dated Garrison Kane for the sole purpose of making Deadpool jealous.
Shapeshifting: Copycat is able to change her shape, taking the form of any human being she sees, she is also able to use that shapeshifting to heal to an extent, such as closing wounds on her body, it has been made clear she can not heal from certain things, such as Slayback's T-O Virus.. which leads us to her secondary mutation...
Power Mimicry: Copycat's powers take her to a level above Mystique, she is not only able to look like someone, but able to copy them completely, even their powers. She notably demonstrated this by copying Deadpool's healing factor to counter Slayback's T-O Virus.
It has been speculated by fans, but not confirmed by Marvel, that she may be Mystique's daughter and Nightcrawler and Graydon Creed's sister.
In Other Media Edit
Copycat or rather, her alter ego Vanessa, appears in the live-action 2016 film played by Morena Baccarin. (What the shit!!? Leslie Thompkins from Gotham? Awesome!!) In this variation, she is a stripper/prostitute who meets Wade in his hangout, Sister Margaret's School For Wayward Children. What started as a business date, blossomed into a full blown (If not, worthy of it's R rating raunchy.) romance, based on their similar personalities and traumatic childhoods. When Wade finds out he has cancer, Vanessa tries to be supportive and get him treatment much to his reluctance and he gets his healing factor in an attempt to cure his cancer, resulting in his disfigurement. Unlike her comic counterpart, Vanessa does not have shapeshifting powers that we know of. (Though judging by that one scene, she may have. You know the one I'm talking about.)