After much speculation, Warner Bros. has confirmed that Deathstroke will be a fully playable character in Batman: Arkham Origins' challenge mode, but only if you pre-order (though I'm sure you'll be able to buy it for a small cost if you decide to wait).
Either way, Deathstroke, who had a major role in today's Arkham Origins trailer, will be playable in the popular mode which tasks you with completing a series of, well, challenges. The Deathstroke pack includes unique weapons and special moves. He will be playable in all challenge maps in the game, as well as two additional challenge maps that are included with the pack that have not yet been revealed. The pack also contains two alternate Deathstroke characters skins.
Batman: Arkham Origins is set to release worldwide on Octboer 25, 2013 for Xbox 360, PS3, Wii U, and PC. There's no talk of next-gen consoles, but there is Batman: Arkham Origins Blackgate heading to Vita and 3DS.