Gaster

The dungeon's capital. It contains Asgore's house and throne, where he either fights or drinks tea and discusses important matters regarding the economy and the state of the kingdom. The hall is filled with golden flowers in honor of the king and queen's deceased daughter.

This is a snowy location. It's quite cool and very cute. Sans, Papyrus, and many others live here, including Logami and Doganessa (married dogs), Doggo the bartender dog, Lesser Dog (a small dog in large armor), and Snowdrake the bird (these are just mini-bosses).
There are many locations: the library, Sans and Papyrus's house, and Grillby's Bar. Grillby's Bar is a bar that sells small snacks and booze. It's sold by Grillby the Silent Light.

where all the monsters live
.. and even people. There are 4 locations: Ruins, Snezhnograd, Vodopadye, and Zharozhemye.
And some small things: a new house where Asgore lives. MTT resort, core, true laboratory. Many years ago, wars broke out between monsters and humans, humans won and imprisoned humans under Mount Ebott. Monsters need seven human souls to open the barrier.

This is an anthropomorphic fish, part of the royal guard. Yellow teeth, a black tank top, blue jeans, and red boots. She has blue skin and red hair tied in a bun. She is also Alphys' girlfriend. Yes, she is a lesbian. Weapon: a blue spear. She can be rude, but she is brave and courageous, kills people for Asgore, and doesn't really like Mettaton.

Queen of the Underground and loving mother of Asriel. She was divorced from Asgore for a long time, but later forgave him. The reason for the divorce was the death of six children's souls at Asgore's paws, as they were needed for the Underground. She is an anthropogenic goat with white fur and pink horns. She has a large body shape. She wears a purple dress with the Underground crest. She goes barefoot. She loves to bake butterscotch pies for the family. She cherishes Chara and Asriel, but Chara dislikes this. She loves her children and her husband, Asgore.
A very caring and understanding mother. Her weapon is fire. She is very afraid of hurting anyone.

Gaster's youngest son. He is 18 years old and quite tall, well, taller than his brother. He is very positive, proud (not really...) and caring. He has a thin build and is also a skeleton. He wears a red scarf, a white short-sleeved vest, blue shorts, red mittens, red boots, a black fitted tank top under the vest, and black tight long johns. He is quite handsome and very friendly. He speaks LIKE THIS and likes to say "Nye-he-he", "nya-ha-ha", etc., which means laughter. He loves Sans, although he always grumbles about his jokes and laziness. He really wants to join the Royal Guard, but is too soft and timid for that. He is friends with Undyne, and she trains him.

Gaster's eldest son. He's 25 years old and quite short. He loves to make lame jokes about bones and skeletons. He always smiles with teeth. He physically can't help but smile. He's also a skeleton. Sans's eyes are black, and the pupils themselves are white. He wears a blue jacket, a white T-shirt underneath, black shorts, and white sneakers. He's quite lazy, but his laziness doesn't stop him from being smart, helping his father, and loving his brother more than himself.

The royal scientist. He is 43 years old (but looks 20) and is very smart. He is usually stern and serious, but can communicate quite nicely if you please him. His height is two meters and Gaster's body is quite thin, but tight. Gaster has a white mask on his face. But somehow the mask's mouth can move, and the eyes blink and widen. It has slits under the left eye and above the right. The mask expresses completely black sad eyes and a black smile. The scientist also wears glasses, a white academic coat, a jacket under it, black fitted pants and shoes. He communicates using the Windings language and used to speak with his hands, but now he has learned to write and speak perfectly. Gaster has two sons, but no wife. No one knows where she is. By the way, his palms can be removed from his hand and multiply. They have one hole in the middle.