Universe Sonic

Infinite views Sonic not as a personal enemy, but as an annoying obstacle—one of those interfering with Eggman's plans. When they first met in the Mystic Jungle, Infinite barely noticed Sonic, fighting him with icy indifference. He defeated Sonic with illusions (copies of Shadow, Metal Sonic, Zavok, and Chaos) and captured him.
However, Sonic is the only one who manages to irritate Infinite. Unlike most of his enemies, Sonic isn't afraid of him and responds to his threats with jokes: he asks Infinite his favorite color and "if he likes long romantic walks on the beach." In the English version, Sonic directly calls Infinite a "clown" and says the grave will be for him, not Sonic. This offends Infinite precisely because it hits his insecurities—Sonic doesn't show the fear that Infinite so desperately needs.
Infinite, for his part, tries to break Sonic psychologically: he creates the illusion of the Resistance's complete defeat, lures Sonic and Avatar into the "Null Void," and helps Eggman create a virtual sun to incinerate the entire Resistance army. But each time, his habit of underestimating his opponent and delaying the pleasure instead of delivering the decisive blow fails him.

Infinite was the leader of the mercenary group Jackal Squad, with a fearsome reputation. During a raid on Eggman's base, the Phantom Ruby revealed to Eggman the Jackal's wish—a ruined world. Eggman proposed an alliance, and Infinite accepted, forcing his squad to join against their will.
Later, while guarding Eggman's facility, the squad was wiped out by Shadow, and Infinite himself was easily defeated and labeled "useless." This humiliation broke him: in a fit of hysterics, he merged with the completed Phantom Ruby prototype, donned the mask, and destroyed his former identity.

With renewed vigor, Infinite became Eggman's right-hand man: he defeated Sonic and helped Eggman conquer 99% of the planet in six months. But the Resistance freed Sonic, and in a series of battles, Infinite lost—first to Sonic, then to Sonic, and in the final battle, he lost Phantom Ruby.

An anthropomorphic jackal with black fur. Long, stiff white dreadlocks, a white ruff of fur around his neck, and white stripes down his back resembling ribs. A fluffy tail with a white tip. Black gloves with silver stripes and pointed fingers; black metal boots with an infinity symbol on red soles.

Heterochromia: the right eye is blue (crossed by a large white scar), the left is yellow. Prominent fangs, black nose.
After fusing with the Phantom Ruby, Infinite wears a silver mask with large ears adorned with black and white circular patterns. Her left eye is visible through a red visor, while her right eye is covered by a black, lightning-shaped plate that glows red when she uses her power. The ruby ​​is implanted in her chest. When she activates her power, her body is enveloped in a red aura with glitchy, pixelated particles.

Personality
Before his transformation, Infinite was a cruel, heartless mercenary, proud of the title of "the ultimate mercenary." He openly encouraged his subordinates to kill, showing no remorse. Beneath his bravado lurked a nihilistic desire: to see the world destroyed—a desire the Phantom Ruby revealed as his deepest desire.

After being defeated by Shadow and merging with Ruby, his character changed radically.
Cold and collected - outwardly unperturbed, speaks theatrically and formally, instead of the previous rudeness.
Extremely sadistic - enjoys the fear of others, calling feelings of horror and doubt "delicious."
Arrogant - considers himself invincible, despises everyone except himself.
An inferiority complex is his main trait. The humiliation from Shadow was the starting point: Infinite can't stand the slightest hint of his own weakness, which is why he abandoned his former face and donned a mask.

Silkadoom is a fan-made antagonist from Sonic RPG. He was created by Doctor Eggman, who combined Sonic and Shadow's DNA with dark energy to create the ultimate fighting form and take over the world. Immediately upon awakening, Silkadoom rejected his creator, renaming himself, and revealed that he sought not service, but absolute power. Due to his power, a panicked Eggman opened a portal and sent Silkadoom, along with Sonic, Shadow, and Knuckles, to the world of Herbegitan. There, Silkadoom formed an alliance with the ruler of the dark side, Reala, and continued to plot to seize energy and territory. He repeatedly clashed with Sonic (including his super and hyper forms), achieving temporary victories, but was eventually defeated due to the depletion of his energy and the intervention of Sonic's allies. After each defeat, Silkadoom swore revenge on Sonic specifically, as the one who "should never have defeated him."

Nazo is the embodiment of the negative energy of the Chaos Emeralds, appearing in the fan project Nazo Unleashed. His goal is to absorb maximum power and destroy the Master Emerald, dispersing its energy across the galaxy and becoming invincible. Nazo acts on a grand scale: he doesn't simply fight heroes, but causes planet-wide destruction, reveling in the chaos. Sonic proves to be one of the main obstacles in his path: Nazo views him as an annoying barrier to be destroyed demonstratively and mercilessly. In fan-made sequels, Nazo repeatedly returns to his plan to destroy the Master Emerald, and clashes with Sonic become stages in this grand goal—each time Nazo tries a new form (Ultimate, Ultimate, Chaos), growing in power.

Silkadum
Appearance. An anthropomorphic hedgehog. His design is a mix of Sonic and Shadow: his fur is predominantly black, but his spines have blue markings (Shadow's), and the skin on his arms, stomach, and inside his ears is tan (Sonic's). His spines have an interesting feature: the top and bottom ones point downward, while the center ones curve upward. Silcadum wears dark gray striped boots and white gloves.

Personality. He is a hybrid doppelganger created by Doctor Eggman by fusing Sonic and Shadow's DNA with negative chaos energy. Silkadoom has absorbed the negative traits of both, and amplified them under the influence of the dark energy. However, he lacks the heroic spirit of Sonic or Shadow in their classic versions. He acts cruelly and calculatingly, seeking to seize power (for example, in the NiGHTS dimension) by any means necessary.

Silkadoom views Sonic as his archrival and an object of humiliation—and, in part, as a "distorted reflection of himself." Because Silkadoom is created from Sonic and Shadow's DNA, plus the negative energy of Chaos, he possesses something of Sonic's own, but inverted: instead of a desire to protect and help, he possesses a desire to dominate; instead of ease and excitement, he possesses a cold cruelty.

In fan fiction (such as Sonic RPG), their relationship is a constant duel of ambitions: Silkadoom openly mocks Sonic, hurls arrogant remarks at him, and taunts him about his speed and new forms (like Hyper Form). He believes that "true power" comes from destruction and energy control, and that Sonic's ideals are a weakness to him. Silkadoom doesn't just want to win; he wants to prove himself superior to the original from which he was created. After defeats, he becomes enraged and promises that Sonic will "pay" for the blows he inflicted.

Nazo
Appearance. In his base form, Nazo resembles Super Sonic, but with a bluish tint from the Chaos Emerald. He has light blue fur and bluish-white spikes that point upward. His eyes are white and pointed, with green irises and black lines at the corners. He wears red and blue boots with white cuffs and white gloves with the same cuffs.

Personality. Nazo is the embodiment of the negative energy of the Chaos Emeralds. He is driven by the desire to become the most powerful force by absorbing as much energy as possible. He views the Master Emerald as an insurmountable obstacle (a source of "infinite" energy) and plans to destroy Earth in order to shatter it and disperse its energy across the galaxy. Nazo is dangerous and cold: he takes pleasure in destruction (for example, smiling after destroying a city). He is confident in his own strength and sometimes underestimates his opponents. In his most exalted forms, he revels in his power and begins to cruelly "toy" with his opponents. However, his judgment is often distorted by the influence of power, which ultimately leads to defeat.

He views Sonic as just another obstacle on his path to ultimate power. Nazo is the embodiment of the negative energy of the Chaos Emeralds, and his goal is to absorb as much of that power as possible, ideally by destroying the Master Emerald and dispersing the energy across the galaxy. Sonic isn't a personal enemy to him, but one of those trying to thwart this plan, so Nazo acts with the utmost ruthlessness.

In Nazo Unleashed and the fan-made sequels, Nazo doesn't waste time on long conversations: he immediately displays overwhelming force to break his opponent's will. He can smile after wreaking havoc and toy with his enemies when he feels superior—and Sonic is no exception.

At the same time, Nazo underestimates Sonic precisely because of his overconfidence: he believes that no speed and no allies can stop the flow of his destructive energy.