His Personality:

Being Sonic's polar opposite personality-wise,[5] Shadow is, bluntly put, a brooding loner. He usually acts with a cool and businesslike indifference, only occasionally showing his vulnerable side. He is rarely seen with others for an extended period of time and usually distances himself from essentially everyone. He is usually blunt and does not speak much, but he always knows exactly what to say in combat. However, Shadow never bluffs; if he makes a threat, he has every intention of carrying it out.

Shadow also does not mind boasting about how powerful he is, calling himself the "Ultimate Lifeform" and, like Sonic, can be extremely arrogant, often belittling his opponents and insulting their lack of strength. He believes no one can beat him and tends to see anyone as a fool for challenging him. Shadow also has a ruthless and merciless edge in combat that most other characters in the series lack and displays a natural "killer instinct".

As the most violent and merciless character in the series at times,[5] Shadow's ruthlessness and aggression leads to enemies never treating him lightly; he is one of the very few individuals Sonic takes seriously. Alongside his dark and violent demeanor, Shadow can be smug and stubborn. He treats others in a very callous manner, throwing in his opinion no matter how cold-hearted it is and not caring for whatever the response is. Shadow is also shown to have a sharp wit; in Sonic Adventure 2, after being called a faker by Sonic, he replies that Sonic is not worth being considered his fake. In Shadow the Hedgehog, he similarly taunts Black Doom's eye for having trouble with GUN. This attitude is reflected in the original Japanese version, where Shadow omits honorifics and speaks highly of himself (if not rudely). At the same time, however, in Japanese, he normally uses the "boku" pronoun when referring to himself as opposed to the more arrogant/confident "ore" pronoun (which characters such as Sonic and Knuckles use).

Just like how Shadow's motivations are never simple to understand, he spends as much time grappling with his own inner demons as he does with his rival, Sonic.[5] In the past, Shadow has had a degree of mental instability, in particular post traumatic stress disorder. This was demonstrated by his instances of post-traumatic flashbacks to Maria's face prior to and during the events of Shadow the Hedgehog, though it could be argued that the instances of the latter game were simply an effect of his amnesia. On one occasion, in Sonic Adventure 2, seeing police sirens flashing caused him to intensely flash back to the massacre aboard ARK and in particular Maria's death. Shadow was soon able to overcome this in his his own game and in Sonic Battle, during which he chose to move on from the past, yet keep Maria in his heart. In fact, his personal journey since being awoken by Eggman has had him confront the shackles of his past, such as ties, fate, and memories. Since then, it appears as though he is reaching a point where he can "do as his heart desires" in his own way.[15]

In many games Shadow is featured in, he pursues his foes with a relentless, unwavering determination. He will usually go to any length to accomplish something he desires or feels should be a certain way, no matter what the cost. In Sonic Forces, it is heavily implied that Shadow ruthlessly massacred an entire mercenary band not only in an extremely dismissive, nonchalant manner (as he did not even remember the incident a few months later), but also seemed slightly proud, mocking the mercenary defense squad by saying they themselves needed a defense squad. He also demonstrated rather coarse language in his own game.

Shadow possesses a strong sense of identity; after falsely being told by Rouge that he isn't the Ultimate Lifeform due to a lab report, he states to her that even if his memories were fake, he is still Shadow the Hedgehog. Similarly, in Sonic Heroes, during the Egg Fleet level, he mentions that, even without his memories, he is still the Ultimate Lifeform, Shadow the Hedgehog. These qualities make him rarely susceptible to being manipulated by others.

In Shadow's own words, he is not interested in peace, nor does he care about what happens to others. In truth, he simply does not like when foolish people do whatever they please. While this may make it seem like Shadow stands firmly in opposition to villainy, he is actually very indiscriminate about who he faces, as he choses to stand against anyone who he condemns for being foolish, be they villains like Dr. Eggman or heroes like Sonic. He similarly does not want thanks for the help he provides when he does something heroic, believing that showing gratitude is a waste of time.[15] Despite his apathetic nature, however, Shadow is not without compassion; since reforming himself at the end of the Space Colony ARK incident, he has ultimately fought for the greater good. When Omega begins his attack in Sonic Heroes, Shadow could have easily forgotten about Rouge and engaged Omega without defending her, but instead saves her from Omega despite having absolutely no memory of her. He was also shown to be legitimately shocked when he learned that his goal of gaining the Chaos Emeralds to restore his memories was actually manipulated by Black Doom in order to wipe out humanity. Likewise, when the Commander finally confronts him with his own memories of Shadow's nightmarish creation, Shadow agrees to face judgment if he was indeed responsible for the ARK massacre 50 years ago. In Sonic Colors, Shadow was also shown to be worried about the possibility of Sonic and Tails getting hurt while trying to save the Wisp, much to their surprise. However, he ultimately remained dismissive about his concern for them.

Shadow is often depressed about the loss of Maria, which is why he keeps to himself, but his relationship with Maria is obvious as he goes to great lengths to protect the planet and keep her dream of peace and prosperity alive. He also maintains a strong bond with his teammates, Rouge and Omega, proving that while his attitude makes him seem like a careless person, he does have some compassion, more than he otherwise lets on. Still, Shadow brushes off most kindness or sympathy that is sent his way; in Sonic Heroes, when Rouge showed concern for Shadow when he saw a broken android of himself, suspecting Team Dark's Shadow might be an android too, Shadow curtly brushed her concern away. In Shadow the Hedgehog, after Sonic suggested some "friendly competition," Shadow bluntly rejected his offer. At times, however, Shadow is shown to appreciate genuine care. In Sonic Adventure 2, after Amy made him remember his promise to Maria, Shadow openly decided to keep his promise to protect the planet both to Maria and her. Another instance is in Sonic the Hedgehog (2006), when Rouge told him that she would always be by his side, he acknowledged her.

Despite the fact that Shadow often fights for the greater good, he is considered an anti-hero for the most part due to his morality and means to his desired end goals. He does whatever is necessary to get what he wants or feels is right, though this enthusiasm causes him to take risks and jump into situations without fully thinking it through.[16] Alongside Rouge, he has also taken prize money and jewels upon winning in Sonic Free Riders. He and Rouge disregard the opening and closing ceremonies for the Grand Prix, showing up late without a third teammate and, if they win the Grand Prix, starting to walk off right away with what turn out to be dummy versions of the prize money and gems. Regardless, Shadow does have his moments of selflessness and heroism; he nearly sacrificed his life at the end of Sonic Adventure 2 to save earth, and helped Silver uncover the truth of the Solaris Project after saving Sonic from him in Sonic the Hedgehog (2006).

Ref: https://www.youtube.com/watch?v=gUGoL6n8XHI