Green Gaster (the goner)

Chris secretly works for Gaster, while pretending to be the main character.

Ralsei is one of the three heroes mentioned in the legend of Rune Delta and formally holds the title of "Prince of Darkness." Ralsei is a short, monster-like character (Darkner). In the first chapter, he wears a pointed green hat that obscures his horns and face, making his fur appear black. He wears a long green coat with a black heart on the chest, round green glasses, and a long pink scarf.
When Ralsei removes his hat at the end of Chapter 1, his face is revealed to resemble the boss monster Asriel from Undertale, but with pink horns and pink fur accents. Without his glasses, his eyes are pink, with pronounced eyelashes and pink eyeshadow.
In the second chapter, the details of his clothing change: the sleeves of his coat become black, and an inverted spade appears on his chest instead of a heart. Another enemy of Gaster

There are three heroes of darkness who stand in the way of Gaster's plan to destroy Deltarune. According to an ancient prophecy (the Legend of the Deltarune) in Deltarune, the three heroes must restore balance between the Light and Dark Worlds. The prophecy identifies them as the Human, the Monster, and the Prince of Darkness. Here they are:
Chris is the only human in a city full of monsters. He serves as the squad's tactician and leader, and in the Dark World, he wears blue armor. In the Light World, Chris is a teenager with yellowish skin and long brown hair that often covers his eyes. He wears a light green sweater with a yellow horizontal stripe and long sleeves, brown pants, and brown shoes.
In the Dark World, his appearance changes: his skin takes on a bluish tint, and his hair turns dark blue. He dons silver armor (shoulder pads, cuirass, gloves, and boots), revealing a dark blue bodysuit underneath. A pink and blue cape is slung over his right shoulder.
Susie is a school bully who, in the Dark World, becomes a powerful fighter wielding a huge axe. Her personality gradually changes: from an aggressive loner, she transforms into a loyal friend. Susie is a tall, reptilian monster, vaguely reminiscent of a dinosaur. She has purple, scaly skin, long, tousled eggplant-colored hair, black pupils, and yellow sclera that can glow in the dark. She has freckles on her cheeks, and sharp, yellow teeth. In the Light World, Susie wears a long purple cardigan, a white T-shirt, ripped, baggy jeans, and black boots. In the Dark World, her appearance changes: her skin becomes lavender-pink and her hair is plum-colored. She wears a dark vest with purple trim, a purple sleeveless shirt, baggy, plum-colored pants, and black boots with gold soles. She also gains black bracelets with yellow spikes on her arms, and a large golden heart-shaped buckle on her belt. Susie is Gaster's enemy.

The Normal NPC is a minor character in Deltarune, a resident of Hometown. He is a bird-like monster with blue plumage and yellow stripes on his neck, wrists, and torso. He is actually Gaster's secret servant and his follower from another world. Fans speculate that the Normal NPC may have killed Onion-san to prevent him from revealing the secret of the "song from the sea." He fed Onion-san to everyone in Hometown, making takoyaki out of him. There are also theories that he is a "goner" (a monochrome NPC from Undertale who narrates Gaster's story).
Aqua is a character from the game Deltarune, the secondary antagonist of Chapter 5. She is one of the seven multicolored flowers. Aqua appears as a little girl with sea-green skin and long black hair that curls like devil horns. Her bangs conceal one to three large red eyes—the number varies depending on the situation. She wears a large sea-green dress with a red collar, red shoes, and a red heart-shaped ribbon in her hair. She is childishly naive and playful. No one knows what this little girl does in the Gaster Cartel, but she enjoys hanging out with everyone and sailing the seas of nothingness.
ERAM, or Shadow Mantle, is a bonus boss who appears in Chapter 3 as the final opponent of the hidden "Way of the Sword." He appears as a mysterious figure in a black cloak with horns and an orange mouth. He is a close companion of Friend, and they collaborate in battle.

Gaster has his own personal cartel, or crew, that supports him in everything. Rumor has it that Gaster used to be a pirate and sailed the seas on his own ship. And his entire gang was with him.
Participants:
-Gaster's followers are gray, colorless entities.
FRIEND / Mike is a mysterious feline entity from the game Deltarune. He serves as a recurring but subtle antagonist, watching over the main characters from the shadows. FRIEND most often appears as a disembodied, smiling face with different-colored eyes (the left eye is pink, the right is yellow) and a wide, crooked grin. He is Gaster's right-hand man, assisting him in everything. He is also Gaster's cat.
The Knight appears as a tall, thin silhouette, black with white outlines. His helmet is diamond-shaped, and his visor resembles a toad's head, but can change shape, becoming either an eye or a mouth. On the sides of his helmet are two long protrusions, resembling sharp, three-pointed horns. His body is slender and angular, with large triangular shoulder pads, a very thin waist, uneven hips, and pointed legs with no visible feet. His palms have large white holes that can emit purple star-like beams, attracting nearby objects.
The Knight's body is shape-shifting: he can curl into a small ball to quickly dodge attacks or transform into a bird-like creature capable of high-speed flight. When receiving sufficient damage, his body deforms, resembling analog static or the vibrations of a seismometer. When the Knight roars, his appearance becomes even more monstrous: two white eyes and a mouth with sharp teeth appear, and his chest opens up, revealing bony ribs radiating outward, revealing a large white eye with a slit-like pupil in the center. He wields a shadow weapon that appears to be either a bat or a sword.

WD Gaster is a nuclear entity or pirate captain who helms a ship in the Dark World. According to Undertale lore, Gaster was the royal scientist of the Underworld before Alphys. He is believed to have created the Core, the energy source for the entire Underworld. Players learn of his fate through dialogue from so-called "Gaster Followers"—NPCs that appear near elevators in Hotland at certain "fun" levels. After falling into the Core, Gaster entered a void where he eventually created a new world called Deltarune.
Description of this figure:
black and green color;
tall, semi-oval body, mostly black;
under his head is a green sweater, dressed in a black jacket, his head is noticeably cracked, two eyes with small green pupils, a wide smile, cracks connect the left eye to the mouth, and the right eye has a crack that runs along the entire head, two green hands with black palms or holes in the palms.
He used to be white, but after falling into the core, he became a "skunk" and turned green. He lives in a bunker. He owns Hometown's nuclear arsenal and dreams of blowing up the town with his nuclear Mike-bomb. He has his own personal cartel. He used to be a pirate captain.