I dont know why but here is BILL CIPHER LORE:
Bill cipher is a dream demon, over trillions of years old and from the second dimension (called Euclidiya).  He was born with a " special ability" though, unlike the other euclideans. He had the ability to see the third dimension and he was basically immortal and all-powerful and stuff so he destroyed his dimension, yes, including his parents. He then decided to live in the nightmare realm and met his new friends, called ,, The henchmaniacs ". They wanted to take over earth because the nightmare realm wasn't completely stable anymore so Bill decided to trick  humans into making a portal for them and eventually he found Stanford Pines who actually did do it but...he found out soon enough about bill's evil plans but after 30 years later Bill gets summoned and he finds the person who has the rift ( some little ball that if it breaks Bill's dimension floods into earth ) and he gained a physical form by that. And then he like got " defeated " but he had a deal with the Axolotl, a god who controls space and time so instead of dying he got into a rehabilitation dimension, called ,, The Theraprism ". He'll be there for many years because I honestly don't think he'll rehabilitate. Anyways, he wrote ,, The Book Of Bill " in The Theraprism and published it and now we can go buy it ✨✨(I already did.....!! For 22 euro...🥰🥰)  ANYWAYS, there is much lore in that book. He had an obsession or crush on Stanford since he LITERALLY got DRUNK because Stanford cut off their deal. Anyways, his personality:
Sadistic, cocky, charismatic, sarcastic, evil, funny, yellow, chaotic, insane
He likes silly straws.

there's no use. It's all gone........

The dimension is goneeyy woneeyy

I will draw him in school tomorrow.