Sonic and Shadow

Shadow has been noted to resemble Sonic, though he is notably different in appearance. He is a black-furred anthropomorphic hedgehog. He has red eyes, a patch of white fur on his chest, a black nose, a tan muzzle and small and triangular ears with tan canals. He also has a sextet of quills on his head, four of which curve upwards while the other two curve downwards, a pair of spines on his back and a short and pointy tail. He has red stripes on each of his head quills, around the edges of his eyes and on his arms and legs.
For attire, Shadow wears white gloves with black cuffs and red tongues, and Air Shoes which, like his gloves, have black cuffs and red tongues. Shadow also wears Limiter Rings, one on each of his wrists and ankles.
Being Sonic's polar opposite personality-wise, Shadow is, in simple terms, 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 as a natural introvert. 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.
As the most violent and merciless character in the series at times, Shadow's ruthlessness and aggression leads to enemies never treating him lightly. Alongside his dark and violent demeanor, Shadow can be smug and stubborn. He usually 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.
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.
He likes to eat coffee beans raw.
Shadow's Limiter Rings and Air Shoes are meant to act as mobility and focus aids, analogous to those used by disabled people.

Sonic:
Sonic is an anthropomorphic hedgehog with blue fur that covers most of his body, and peach skin on his arms, muzzle, insides of his ears and front torso. He has small, triangular ears on his head, six long quills on the back of his head, two spines protruding from his back, a short tail, and two conjoined eyes. For attire, he wears red shoes and white gloves.
Sonic is described as "like the wind", a free-spirited drifter with an insatiable appetite for adventure. He values freedom above all else and lives by his own rules rather than societal standards. Sonic's primary passion is speed, and he likes anything that is fast.
Sonic loves traveling around the world, interacting with different cultures present on the planet, and tasting regional dishes, particularly chili dogs. He never stays in one place for long and always seeks his next challenge, viewing life as a never-ending series of adventures. Sonic hates being constrained, which tends to make him very uneasy and restless. However, he has shown the ability to remain calm even after six months of imprisonment onboard the Death Egg. Despite his love for the outdoors, he enjoys quieter activities, such as reading on rainy days.
Sonic has a calm and carefree demeanor but can be impatient, impulsive and short-tempered. He can be reckless and quick to act before thinking, acting before thinking and ignoring others' warnings. Nevertheless, he is honest, fearless, and always keeps his promises.
Sonic can speak all languages, because he communicates with his heart.
Sonic is a romanticist, and not a daydreamer.
Sonic will never show tears of true grief to anyone.
Sonic does not have parents.
Sonic's quills will raise if he shows surprise, much like an actual hedgehog.
It is implied that even Sonic does not know the source of his own super speed, as evident by his response to the Flash asking him where his powers came from.
Sonic doesn't know how to swim, and he highly dislikes water.