Deathstroke/Arkham Origins

Arkham Origins Deathstroke can be unlocked through Challenge Mode. Otherwise, he can be obtained randomly from Challenge Booster Pack, the newly-added Apokolips Darkseid Challenge Pack and the Arkham Pack, or as a guaranteed character from the Arkham Asylum Pack. However, obtaining him from a pack will not unlock him for direct promotions.

Strategy
Words alone cannot begin to explain the epicness of this card. Arkham Origins Deathstroke is the ultimate damage dealing machine. His less than usual base damage for a Gold card may seem unsettling, but every time he is promoted he gets 8% additional damage, adding up to a staggering 56% at Elite VII, or with the equivalent of 1326 damage. Upon reaching 200% (which has a wider area and is significantly easier to hit), his Point Blank will deal CRIT (Critical) damage and will be unblockable, which at the least takes off half your opponent's health with a single Special 1. This Deathstroke is the ultimate damage dealer; given Crit boost gear this card can level opponents in one special, and his second attack can knock out entire teams. When fighting against him, you better have a power drain character or gears on you; one or two Point Blank attacks and you're done. Also noted, if the opponent blocks, the first hit that becomes UNBLOCKABLE will NOT be a crit, but the following hits will be.

Gear
Promethium Longsword is core on Arkham Origins Deathstroke, as he can make great use of all its stats. Cloak of Destiny is a fairly common option, and while it can be used to great effect, it is not very necessary on him and would be better used on someone else with better synergy with it, and isn't a particular goal to work for if you are using AODS. Mutated Bone Spikes (Doomsday's gear) is a fairly simple and safe option given his affinity with basic attacks and his s1. It can be combined with Promethium Longsword and any basic damage/crit gear for a cookie-cutter and relatively easy to achieve Deathstroke build that does tons of basic damage. The Ibistick is another decent choice as it gives great power generation and s1 damage increases. Ra's Al Ghul's Scimitar is a great pick as it gives him a bar of starting power to devastate the enemy team swiftly. While Deathstroke has a 2-hit combo ender, it may not be very practical to try and use it for the power drain, as his light basic attacks have poor range compared to his heavy attacks. On the other hand, his heavy attacks have a very long recover animation (i.e. if the first hit is blocked, he takes a very long time to recover before he can block). LexCorp Helmet Armor V2 and League Of Assassins Adept Hood can be used for their crit boost, but the former's other stats don't fit him well while the latter's do. League of Assassins Adept Knives (also from the League of Assassins Set) can be used increase power generation (to be able to use your sp1 faster), increase the damage of his sp1, and also deal immense damage to the entire enemy team as well. With the 2.6 update, the ability to allows your character to augment their stats (damage, health, Crit chance and Crit damage) to make them stronger, thus making him an even more dangerous threat with crit boost gears!

Good with

 * Harley Quinn/Arkham: She gives Arkham teammates a 50% block breaking chance on every hit of their s2. AO Deathstroke's s2 hits six times; it is essentially about as good as unblockable, making a Deathstroke at any level of power above one bar an unavoidable barrage of pain.
 * Deadshot: ​His passive increases the "sweet spots" of Target special moves after Deadshot has used his Special 2, after it has been used, both of Deadshot's teammates who have Target specials also receive the boost to their "sweet spots", increasing Deathstroke's already high damage even more. Despite so, even upon reachin 250%, the damage would still remains the same regardless of Deadshot's passive, although the main benefit is that, instead of reaching the "regular"  166%, it will now be 199%, which actually does increase the damage!

Countered by

 * Green Lantern/Red Son: Green Lantern's passive grants crit immunity to each Red Son character on his team and reduces all special damage that each would have taken by 20%, and thus can severely dampen Deathstroke's damage output against potentially all three of his opponents.
 * Black Adam/Regime: Black Adam can reflect the damage of up to 3 hits from Deathstroke's s1 back at Deathstroke doubled.
 * Raven/Prime: Deathstroke's powerful multi-hit specials will almost inevitably trigger her passive, causing her to swap health percentages with Deathstroke.
 * Superman/Injustice 2, Riddler's Staff, Batman/Dawn of Justice, The Flash/Reverse Flash: All of them have a chance to completely "evade" Deathstroke's SP1.

Abilities
Here are Arkham Origins Deathstroke's abilities.

Support Cards and Gear
Here are Deathstroke's support cards and gear.

Trivia

 * Upon release, the defense AI always achieved 200% on his special 1, including in multiplayer, making him absurdly difficult to fight against. This was changed after player complaints, and he now only occasionally hits 200%.
 * The leaked version of Green Lantern/Red Son (which was released 3 characters after Arkham Origins Deathstroke) did not have his current passive. It was suspected it was changed to include immunity to crits to give players an option to counter AO Deathstroke.