In Mercury's first appearance in "Black and White", he is shown to be a pale, well-built young man with gray eyes and, while draped in shadow, somehow purple hair (revealed to actually be gray in the credits of the same episode), partially slicked back while unkempt at the front. He also wears a slate gray and black two-tone partial-zip jacket that covers his upper body. He is stated to be in the age range of a Huntsman Academy student.
Mercury's appearance does not change much leading into Volume 2, though his hair and eyes become a silvery-gray. He also wears a single notched belt with what appears to be a sash or bandana draped over it. Protecting his arms are sets of rerebraces and vambraces.
He has prosthetic legs that attach part-way up his thighs. These legs are usually hidden due to him always wearing pants and a pair of shoes. His armor hides what appear to be oddly-shaped scars on the outer sides and backs of both of his arms.
The World of RWBY: The Official Companion describes Mercury as "skinny guy."
In "Beginning of the End", he was first seen wearing his signature zip jacket with the collar zipped all the way up, minus his armor. His pants were dark orange and he wore a pair of black boots.
In "Best Day Ever", Mercury is shown to be rather care-free and jokes around when in the company of Emerald, who he makes an effort to annoy. He seems to opt for excitement and action; he dislikes books without pictures and tells Emerald he finds the city boring. However, when it comes to matters at hand, Mercury drops this and focuses himself on the mission, though his carefree attitude may occasionally slip out during combat, such as when he taunted Ruby Rose during both their encounters once he got the advantage in their skirmish.
During battle, Mercury displays a sense of seriousness and levelheadedness. Based on his fight with Pyrrha Nikos, he appears to test and gauge his opponent before fully committing to an attack, implying he has a strategic mind. His cunning is later shown once more during his match against Coco Adel and Yatsuhashi Daichi in "Lessons Learned", where he takes advantage of the savanna biome to hide before launching a surprise attack on Coco. He also uses the geyser biome to his advantage, using it to create an opening on Yatsuhashi and defeat him.
Judging from the nonchalant way he talks about killing Tukson, Mercury appears to have no qualms about intimidating and killing others, even light-heartedly joking about it afterwards with Emerald. Although subtle, he also speaks in a derogatory fashion about Tukson even after having murdered him in cold blood. This is probably due to his father's tutelage as he was most likely taught in the ways of assassinations.
He also seems to derive personal enjoyment from the pain of others. Whether this is for his own self-satisfaction or to put his opponents in an unstable state of mind to take advantage of their emotions is unknown. Examples of this are seen in "A Perfect Storm" where he attempts and fails at intimidating Raven Branwen and later in "The More the Merrier" when he condescendingly asks Yang Xiao Long and Ruby if they missed their old 'friends'. Later he tells Yang she 'owes' him an apology for his leg before turning serious for their rematch. This side of his personality is also briefly seen in the same episode, as he smirks proudly when Cinder torments Jaune Arc. However, despite his sadistic streak, he is not incapable of caring for others. He takes on a soothing tone when convincing Emerald to retreat from battle while she grieves over losing Cinder.
In "It's Brawl in the Family", he appears to show genuine concern when spotting Qrow Branwen, knowing he poses as a substantial threat to Cinder's agenda and shows total cooperation in letting her know of all the details he can gather.
"Fall" and "Beginning of the End" demonstrate his acting ability, where he plays a major role in framing Yang; he makes it seem she initially attacks and lands a serious injury on him, when in truth, due to his prosthetic legs, the injury is not as grave as everyone else is led to believe. He is also very compliant with Cinder's orders, allowing himself to remain hidden for the immediate future so as to not jeopardize the plan.
Despite his usual carefree demeanor, in "The Next Step", it is shown that Mercury does not take insults or disrespect well, responding to Arthur Watts' insults with an eagerness to attack him until Emerald stops him. This is further shown in "A Perfect Storm" when Raven rebuffs his attempt at intimidating her. He is usually outspoken, but when he is with Salem's group, he refrains from speaking. This was shown again in "Lost" when he lashed out at and attacked Tyrian Callows when the other mocked him for being a child that feels like a "big bad man" and correctly assuming all Mercury knows in life is pain and violence, condescendingly calling his life a 'tragedy'.
Mercury carries an immense bitterness within him due to his abusive upbringing by his assassin father, Marcus Black. This bitterness holds over due to the fact that Marcus used his Semblance to steal Mercury's, which he said would return if Mercury became strong enough, which he proved the moment he killed his father. This turned out to be a lie, and Mercury feels as though he has had to work harder than any other member of Salem's faction due to his stolen Semblance.
Mercury angrily confesses to Emerald in "Lost" that his father abused him physically and emotionally and that he used to constantly beat him up and call it 'training' while telling him that he was weak and relying on crutches, leading to Marcus removing Mercury's Semblance with his own. This coupled with the fact his father was an alcoholic makes it obvious he suffered a miserable upbringing filled with hate and misery. In the same episode Tyrian later alludes that the only reason Mercury is on their side is because of Marcus' influence and that he is now too afraid to leave the few things he knows: pain and violence.
Unlike Emerald, Mercury also realizes that Cinder never truly cared for him and that in the end, their relationship was purely business, possibly because he recognized her subtle manipulations as another form of abuse or he simply always knew he was just a pawn to her.
Powers and Abilities
In the episode "Lost", Mercury reveals that his father stole his Semblance when he unlocked it. His father used his own Semblance to steal Mercury's and claimed that he would give it back when Mercury became stronger. However, Mercury never got his Semblance back despite getting stronger, and after killing his father, Mercury still has no chance of regaining it. Not much is known about Mercury's Semblance otherwise.
As seen in his fight with Pyrrha in "Extracurricular", Mercury is shown to be a very acrobatic and agile fighter who relies upon quickly overpowering his opponent with complex kicks that imply a near-mastery of martial arts that resemble Tae-Kwon-Do. He's also capable of a break-dancing style, similar to Capoeira and make use of Muay Thai as well as shown in the same fight. His experience and skill with his leg-based fighting style is aggressive and effective enough to drive even a fighter of high caliber and great combat experience like Pyrrha, considered to be the strongest first-year student at Beacon Academy, into a defensive position.
He possesses great speed which allowed him to outrun and evade the rapid-fire bullets from Coco's gatling gun even at point-blank range. His strength is seen when he makes Yatsuhachi stagger on his feet and later knocks him out with ease despite the other's towering size and heavy build. His strength and speed is later seen again in "The More the Merrier" when he knocks Yang down with a few kicks and later in "Vault of the Spring Maiden" when he easily disarms Ruby with a single kick after she lunges at him with her scythe's recoil.
Despite his focus on kicks, Mercury also uses his hands to grapple, block or redirect enemy attacks. In his fight with Coco and Yatsuhashi, he grabs them both and twisted them into an easier position for his kicks and even stretches out Coco's arm, allowing him to kick her in the head. During his battle with Yang, he shows deft skill by using his arms to weather Yang's skilled barrage of punches. His skill in utilizing his arms is shown in the same fight as he occasionally punches at Yang before following suit with a barrage of kicks.
Mercury is also known to be observant, tactical and analytical; he notices and deduces the capabilities and limits of Pyrrha's Polarity Semblance after she uses it once during their brief fight. He demonstrates his observational skills once more when he tracks down and counters Ruby's movements when using her Semblance, an ability so fast none of Team JNPR could stop during their brief fight against Team RWBY in "Best Day Ever".
Mercury reveals the impressive extent of skill in the doubles round of the Vytal Festival, dominating both Coco and Yatsuhashi single-handed with his impressive feats of speed and strength, being capable of evading Coco's rapid and dense barrage of bullets and swiftly counterattacking from the air while using the colosseum's biomes to his advantage, showing he is aware of his surroundings and knows how to use them.
Due to his fighting style, Mercury relies on his swift and quick reflexes to counter and block his opponent's attacks as first demonstrated during his fight with Yatsuhashi. He uses certain kicks to alter the course of Yatsuhashi's sword strikes or block them altogether with his greaves. He shows quick reflexes again when he evades Yang by altering the course of her punches, using his footwork to raise her fists and kick underneath or around her attacks.
Mercury's weapon of choice is a set of boots named Talaria that are equipped with a firing mechanism built into them similar to Ember Celica.
Similar to Yang's usage of her Ember Celica, Mercury is capable of firing explosive rounds from his boots whenever he kicks for moderate to long-range combat. Most of the time he's seen firing his boots are usually mid-handspring, also known as a kip/kick-up or when maneuvering his body in a manner similar to break-dancing, more specifically; "Thomas flairs" and "airflares", and is able to fluently translate from his aggressive Tae-Kwon-Do-like kicking style strikes to this Capoeira style. He is also seen using it in a more traditional manner with frontal or side kicks.
Mercury can also control the rounds through Dust use. During his tournament fight, he gathered multiple rounds that spun around him in a manner similar to that of a cyclone surrounding him before the rounds were later unleashed in a devastating flurry. He also possesses, at the very least, capable marksmanship skills, being able to fire his Dust rounds efficiently despite the barrels being located near the soles of his boots, as shown when he fired a round at Yang before using his cyclone technique during their fight and when he shot Ruby's Scroll out of her hands during their confrontation.
He can also use the boots to jump in midair by bringing his legs together and firing his boots simultaneously, boosting him forward and allowing him to achieve temporary flight. This is likely a reference to the Roman god Mercury, known for his speed and ability to fly with his winged sandals.
Mercury has a pair of robotic legs, which he acquired at some currently unknown point in time. His prosthetics make up most of his leg, including a portion of his thigh and everything below the knee. He usually keeps them concealed under his pants. These robotic legs appear to give him enhanced performance in battle, such as being able to withstand blasts of fire without taking damage. He is also able to very easily repair "injuries" to his legs that would otherwise put a normal human out of commission or require medical attention.
His prosthetics are also quite durable, being able to withstand significant attacks that would otherwise severely reduce Mercury's Aura. His prosthetic limbs have so far protected Mercury against a nearly point-blank firestorm, a storm of frozen leaves and a direct point-blank blast from one of Yang's Ember Celica's shells. He used his legs to block a massive strike from Fulcrum that was powerful enough to cause the geyser field biome they were in to erupt; he did this while lying on his back where he had no leverage at all, and he took little damage to his Aura.
His kick-based fighting style, as well as his choice of weapon, are likely intended to take advantage of his prosthetic legs. His prosthetic limbs are capable of firing blasts of air, which he makes great use of in combat.
Among Mercury's skills, his talents at information gathering and subterfuge would appear to stem from his training as an assassin. While undercover at Beacon Academy, he strategically spars with Pyrrha Nikos in order to gather information on her Semblance and combat capabilities to further Cinder's plans to manipulate the Vytal Festival Tournament and initiate the Fall of Beacon. Since Emerald speaks about Pyrrha as if she is the final part of a longer report, it is implied that he and Emerald investigate other students for this reason, as well. Mercury even quotes his father shortly after meeting Cinder, stating that if you need to know a city, you ask the "rats". He is capable of enacting a coordinated strike with Emerald, such as when the duo manipulates Yang into attacking him after her victory in her match with him.
This shows Mercury's skills in deceit, able to put on the convincing facade of a well-meaning - if somewhat cocky - student of Haven Academy.
- Mercury alludes to Mercury from Roman mythology. For more information on this allusion, as well as other choices the creators made for this character, see Mercury Black/Behind the Scenes.
- Gray and Miles described Mercury to J.J. as "a hipster douchebag, but he's cool."
- In an interview with AfterBuzz TV, J.J. claims that if Mercury were going all-out, he would have been able to defeat Pyrrha, though he admits this claim is biased. When describing his voice acting for the character, he says that it is basically him doing a bad impression of Jack Nicholson.