Scorpion/Mortal Kombat X

Mortal Kombat X Scorpion can be unlocked during his challenge. Otherwise, he can be found as a random drop from Challenge Booster Pack, or as a guaranteed character from the Survivor Pack, but neither will unlock him from direct promotions.

Strategy
Rivaling Ares' damage and having a passive that grants health surpassing even the mighty Shazam, Mortal Kombat X Scorpion is a unmovable tank that can deal incredible amounts of damage if used well.

His light combo ender and special 1 will inflict burning damage. His special 2 will inflict bleeding. All of these - including the possibility to crit - are not counted as part of his passive and will work in Dead Zone, making him a powerful character in this field. The damage over time will not apply life drain.

Doom Slice: Part of it deals fixed damage. Only the last hit, a tap and shoot with a widened and easier to hit 200% damage like Deathstroke/Arkham Origins' s1, deal variable damage. Because of this, and that damage over time specials usually have a 0.5x damage penalty, his s2 only does 40%~60% of his damage stat, instead of the normal 60%~120%. The bleed damage deals 6% of his damage stat 6 times (36% total) at 100%, but at 200% it is a rather impressive 18% (108% total), for a theoretical maximum of 168% of his damage stat as total damage.

Other damage over time effects applied by Scorpion will also crit while a crit damage over time effect is running. This includes even the burn from his light basic combo, as well as The Ibistick. The crit (+50%) and the bleed (+20%) (in the case of his s2) stack multiplicatively for +80% damage. In the case of the Ibistick, this will increase its maximum damage from 10% of enemy maximum health to 17.4% (the crit period is very slightly longer than the bleed period, so the fifth hit will crit but would not benefit from the bleed).

Note that while Mortal Kombat X Scorpion's base damage is extremely high, it is somewhat misleading, as his Doom Slice deals reduced upfront damage by virtue of being a bleed special, and his heavy basic combo only does 2 hits but is not compensated in damage like Shazam or Doomsday/Prime (it only does 4% of his damage stat as damage twice, as opposed to 5% + 7%).

Good with

 * Hawkgirl: Her snare on tag in (both versions have it) prevents opponents from tagging to avoid MKX Scorpion's potent damage over time.
 * Catwoman/Batman Returns: Her +100% damage boost to DOT will greatly amplify Scorpion's specials, allowing him to deal a dangerous amount of damage.

Good against

 * Solomon Grundy: Since Grundy's basic attack speed is slow, Scorpion can easily outpace him and deal massive bleed damage.
 * Contrary to popular belief, Green Lantern/Red Son cannot prevent MKX Scorpion from dealing critical damage through his specials.

Countered by

 * Since a max elite (VII) Mortal Kombat X Scorpion has extremely high health, he can be countered by characters who deal damage based on percentage. Examples include Raven/Prime's Demonic Rage and Batgirl/Cassandra Cain's Assassin's Ambush passives.
 * Hawkgirl/Prime: Since Mortal Kombat X Scorpion deals very high damage over time, faster tagging will allow Hawkgirl's team to avoid much of his damage.
 * The Flash: since all of Scorpion MKX's basic attacks are slow, it is easy for any of the Flash variants to interrupt the attack, thus more likely for Scorpion to receive damage than dealing them.
 * Deathstroke: Since all the Deathstroke variants are relatively fast and have longer reach with their swords, chances of Scorpion inflicting basic damage against competent opponents are minimal; moreover, Deathstroke/Red Son boosts the speed of attacks by Red Son teammates up to 15%, making it difficult for Scorpion MKX to land damage-over-time blows.
 * The Arkham Knight: same goes for Deathstroke, since both of his basic attacks has the ability to push the opponent far way and deal damage from long range at the same time, it can make Scorpion have a hard time dealing most of his damage.
 * Superman/Injustice 2: Superman's passive makes him immune to one special move and all effects from it upon tag in. If Scorpion hit Superman with Doom Slice or Flip Kick with the passive active, Superman would be immune to the damage and if Scorpion achieved 200% damage, he would also be immune to the bleeding.

Abilities
Here are Scorpion's abilities.

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

Trivia

 * The Chinese, Spanish, and the Italian versions of Injustice mobile have his passive description mention his burn on combo ender, which the English version lacks. However they also state he extends this effect to his teammates (which is incorrect) and do not mention his bonus health on promotion.