Twisted Functions is an AU similar to Underswap, Storyshift, things like that. It is known as a "Switch Up" AU. It could be called similar to "Inverted Fate" for having the characters personalities staying very close to the same.
In this AU, Monster Kid is the king. His age is heightened to 24 years old. He is awaiting his long lost sister, Alphys, to come back to him.
Monster Kid was trained by Undyne, who died years ago when they fell into the lava of Hotland.
Instead of killing you, he just brings your health down and ends up regretting fighting you, and killing all of the other humans who fell down.
Shiskyren is the character you play as.
When the game begins, it shows that you are a fusion of Shyren's sister and a human. This is because Alphys created you in her lab in the Ruins by fusing a humans soul with Shyren's sister.
Gaster, Head of the Royal Guard
Gaster is the head of the Royal Guard, replacing Undyne, the old leader.
Gaster shoots hands with holes in them at you in many scenarios of the game, such as running from him in Waterfall.
Mettablook is the king's Royal Scientist.
She created the amalgamates.
Frisk the Risky Robot
Frisk is the most famous celebrity in the underground.
She is a human that fell years ago, but is hiding inside of a robot body to keep from people trying to steal her soul.
The Mad Cat
The Mad Cat, also known as Madpants, is a homeless cat who refused to get a job from Frisk.
When you meet him asking for money in Waterfall, there are several things he could say.
If you ignore him and walk away, you get the option to fork up the money, or run off. Running off gives him a white name in the end of the game.
If you only have under 100g when walking by, he will ask you for money, and make you fork up all the money you have if you die while fighting him.
There are many other things he could say as well.
Azzy is a chef at a fast-food restaurant called "Azzy's". He heats up the food with fire magic.
Dummy is a failed creation made a long time before you. The first failed creation.
Lily the Annoying Spider
Lily is the name of the creator of the game. She takes place as a little spider in-game.
Napsta is a jokey, but depressed ghost you meet in Snowdout.
THE TEMSATIONAL TEMMIE
Temmie is the pet(?) of Napsta. Temmie is overexcited all of the time.