The 49-year-old star took to Instagram to share a snapshot from the makeup room, showing his face covered in blue casting putty, while makeup artists Mike Smithson and Bill Corso stood beside him.
"Insanity on the brink. Face is morphing into something machine, fierce, hair sliced, arm machined, bulged," Brolin captioned the behind-the-scenes shot. "Where is Deadpool?!? Looking. Looking. All I got are these two...molding me, prodding, turning me into something hard."
For those unfamiliar with the character of Cable, a.k.a. Nathan Summers, he's a time-traveling, telepathic partial-cyborg with impossibly huge muscles and a vast intellect.
With the short new 'do and the hours he's put in at the gym, the Oscar-nominated star is quickly shaping up to be one impressive Cable.
Brolin will be joining Deadpool star Ryan Reynolds, who will be reprising his role as the Merc with a Mouth, returning stars Morena Baccarin, T.J. Miller, Brianna Hildebrand and Stefan Kapicic, as well as newcomer Zazie Beetz, who's playing the assassin Domino.