As you can see from the full trailer for the next trip to the Arkham-verse from Warner Bros. Games Montreal, Deathstroke is one of several assassins hired, apparently by Black Mask, to kill Batman on Christmas Eve. (We see you, Deadshot.)
Crave's sister site Destructoid stuck around to the end of the trailer to see the Warner Bros. is offering Deathstroke as a playable character if you order the game now.
Deathstroke will boast "unique weapons and special moves" and will be playable in a variety of challenge maps.
Batman: Arkham Origins is scheduled to hit shelves October 25.