Morena Baccarin Will Play Copycat in DEADPOOL
According to a tweet from Baccarin, she's playing a character named Vanessa, which pretty much has to be Vanessa Carlysle, also known as Copycat, a shapeshifting mutant in the Marvel comics universe. Like many of these comic book characters, Copycat has a pretty complicated history, but she started out as a Boston prostitute who met and fell in love with Wade Wilson before he became involved with the Weapon X program. She has blue skin in the comics, so I'm guessing the movie will change her look to avoid aesthetic similarities to Mystique from the X-Men films, since this takes place in that universe.
This isn't the first cast member who has given away his or her character in a Tweet: just yesterday, Silicon Valley star TJ Miller basically confirmed he'd be playing Weasel in the same way.
Deadpool is filming now, and will arrive in theaters on February 12th, 2016.