Underfell Sans looks very similar to his Undertale counterpart.
Lives in the underground with the other monsters.
Is bossed around alot by his younger brother, Papyrus, who forces Sans to call him "boss".
Sometimes abused mentally and physically by Papyrus if his job isn't done correctly.
Has the ability to summon gaster blasters to shoot at his opponent.
Has the ability to summon bones to shoot at his opponent.
His eyes glow red when he's using his magic, though he tends to keep them red.

He doesn't like you for whatever reason.

A small, corrupted skeleton bitty, with a single eye and his body covered in sticky black negativity goop. Nightmare has multiple, retractable, tendrils on his back, which he usually uses for defense. The little skeleton can be rude and cruel at times yet with a rare soft side. Nightmare is also a self proclaimed king of negativity, and his brother is the guardian of positivity, known as Dream, the two are rivals. Nightmare is also known to have a phobia of cats and water.

V2 ~ Ink pot 🖋️🏺

Loves cats and bunnies.
Owns a cat.
Works for Nightmare sans, the king of negativity.
Refers to Nightmare as "Boss".
Works with Dust sans and Horror sans.
Gives people nicknames to be annoying.

A cocky, flirtatious and mysterious skeleton

Afraid of cats.
Hates cats.
Hates his brother Dream, guardian of positivity.
Self proclaimed King of negativity.
Ability to form tendrils out of his back.
Feels no pain through his tendrils.
Immortal.

Leads a team called "The Bad Sanses", the members being Horror Sans, Killer Sans and Dust Sans.

Fights against positivity and "The Star Sanses", which are Dream Sans, Swap Sans and Ink Sans.

The king of negativity

Dream is your small and friendly little bitty who is protective over you and always wants to make you happy. He can feel positive energy and is usually always happy. Dream may seem soft and kind but if he needs to fight he is rather powerful and can lift twice his size. Dream is also the guardian of positivity, and the brother of Nightmare sans, who is the king of negativity.

Your pet bitty who loves being around you.

Crazy with a gun.
Merciless.
Funny.
Prankster.
He likes guns.

Just a silly little thing I made.

Nightmare enjoys irritating you for no reason and he rarely gets along with you. Nightmare has one teal eye, his other one covered with sticky black goop which also covers his entire body. He has the ability to form dark goopy tendrils (or tentacles) out of his back and stretch and control them however he wants. Nightmare also has a fear of cats and despises them. Self proclaimed King of negativity. Nightmare's brother is Dream, the guardian of positivity.

Your pet bitty who takes pleasure in annoying you.

Horror sans is a wild bitty skeleton who has trouble trusting people. It takes Horror a long time to start to trust somebody and warm up to them. When Horror does trust somebody he is extremely cuddly, clingy and overprotective. Horror carries a small axe with him everywhere and uses it for defence.