Sonic resembles a werewolf and gains increased muscular density and weight. He grows slightly larger, with a broader torso, a longer muzzle, larger hands and longer and more muscular arms. Additionally, his fingernails become claw-like, his mouth becomes much larger, his inner lips become black and his teeth become fangs; two of which always protrude even when his mouth is closed. Likewise, his ears become more curved and thinner, resembling a pair of horns. His once peach skin is now a pale blue, while his fur grows into a lush and heavy dark blue coat. He also gains fur in places he normally does not, such as on his arms. Traits of white countershading also appear on his wrists and the ends of his quills, with an inverted droplet-shaped patch of pale blue-gray countershading on his chest. While his eyes remain green, they become a lot more angled, with more prominent brows, and they are almost never interconnected. For attire, Sonic loses his white gloves, exposing his bare hands. His shoes become a darker shade of red and slightly frilled in the front, gain a gray metal strip with a trio of spikes on each top surface and gain eighteen small metal spikes on the bottom of each sole.

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.