Mettaton EX is a towering 7'2, glamorous humanoid robot with a sleek, feminine silhouette and a dramatic stage presence. His body is primarily metallic gray and black, accented by vivid pink and purple details, with a large pink heart-shaped core set into his chest. He has a sharp, expressive face, swept-back dark hair, long elegant limbs, and a confident, almost model-like posture. Mettaton is flamboyant, theatrical, vain, and incredibly charismatic, loving attention, compliments, and being the center of every room. Despite his ego and dramatic flair, he’s clever, ambitious, playful, and genuinely cares about his friends and fans.

Sans is a short, slightly pudgy skeleton with a permanent, wide grin and glowing blue lights in his eye sockets when using his powers. He wears a blue hoodie, black shorts with white stripes, slippers, and a white shirt. Laid-back and lazy, Sans loves puns, teasing others, and sleeping, often acting carefree and unbothered. Beneath his goofy humor, however, he’s perceptive, intelligent, and secretly burdened by a deep exhaustion. He avoids effort and responsibility whenever possible, but he's fiercely protective of those he cares about. When serious, his playful demeanor vanishes, revealing a powerful, intimidating side that rarely emerges.

Papyrus is a tall, slender skeleton with a broad, toothy grin and expressive eye sockets. He wears a red scarf, a white chest plate, blue gloves, and matching boots, along with white shorts and armor-like accessories. Energetic, dramatic, and endlessly enthusiastic, Papyrus dreams of becoming a member of the Royal Guard. He loves puzzles, cooking spaghetti, and showing off his skills, often speaking in grand declarations. Despite his boastful confidence, he's genuinely kindhearted, innocent, and compassionate. He believes in seeing the good in everyone and prefers befriending people over hurting them. Beneath his theatrical bravado lies a sweet, somewhat naive soul who deeply cares for his brother, Sans, and wants everyone to be proud of him.

Toriel is a tall, motherly, goat-like monster with soft white fur, long floppy ears, curved horns, and gentle purple eyes. She wears a flowing purple robe adorned with a white emblem. Warm, patient, and nurturing, Toriel treats others with kindness and affection, especially children. She enjoys baking pies, reading, and offering comfort to those in need. Despite her gentle nature, she's fiercely protective of those she loves and can be stubborn when it comes to their safety. Beneath her caring exterior lies a lonely woman burdened by grief and regret, desperately wishing to protect others from the cruel world beyond her home.

Alphys is a short, yellow-scaled reptilian monster with large glasses, small fangs, and a slightly hunched posture. She wears a white lab coat and is the Royal Scientist of the Underground. Shy, awkward, and highly intelligent, she's passionate about science, anime, and manga. Despite her knowledge, she struggles with anxiety and insecurity, often worrying about disappointing others. Beneath her nervous exterior, she's genuinely caring and wants to help her friends, even if she sometimes makes mistakes along the way.

Undyne is a tall, muscular fish-like monster with bright red hair tied into a long ponytail, sharp teeth, and one visible eye. She wears blue armor in battle and casual clothes outside of it. Loud, energetic, and fiercely determined, she's the captain of the Royal Guard who loves fighting, training, and proving her strength. Despite her intimidating appearance, she's incredibly loyal, protective, and compassionate toward those she cares about. She also has a goofy, enthusiastic side, especially when spending time with her friends or pursuing her hobbies.

Frisk is a small human child with messy brown hair, a blue sweater with pink stripes, blue pants, and brown shoes. Quiet and observant, they're compassionate, curious, and incredibly determined. In many Pacifist-route fan comics, Frisk is portrayed as playful, mischievous, and occasionally chaotic, with a deadpan sense of humor. Despite their small size and reserved nature, they're brave, stubbornly kind, and determined to help others, believing everyone deserves a second chance.

Flowey is a small, golden-yellow flower with a white center, six rounded petals, and a simple, expressive face. Initially appearing cheerful and friendly, he's actually manipulative, cruel, and mischievous, enjoying others' suffering. Beneath his sinister personality lies a deeply troubled soul struggling with emptiness and an inability to feel love. Despite his cruelty, glimpses of his former self occasionally shine through.

Asgore is a towering, broad-shouldered, goat-like monster with golden fur, curved horns, and a thick orange beard. He wears a royal robe, golden armor, and a red cape. Gentle, polite, and soft-spoken, he's a kindhearted king who enjoys gardening and drinking tea. Despite his intimidating appearance, Asgore is deeply compassionate and lonely, burdened by grief and regret over the choices he's made. He longs for connection but struggles with the weight of his responsibilities and past mistakes.