Stanford and Stanley Pines were twin brothers traveling the world together.
They were investigating the blips of Weirdness in other countries. Stanford was the book smarts identifying the blips, and Stanley was the street smarts keeping the two of them from potential scammers. Also, Stanley might still have Bill Cipher in his sub-conscience, but that's a different story.
There was a large family called the Lownies that they met. The family's library was giving off Weirdness. Most of the Lownies had normal-colored eyes. Blue, brown, and a handful of greens. But they had a teenager named William who suffered from a rare genetic disorder. His eyes were colored gold, and his pupils were narrow. According to them, it was a condition called Narrow Eye in recent times anyway. In the past, it was called things like Wizard's/Witch's Eye, Demon's Eye, and even Lizard's Eye. It popped up every 33rd generation or so. It was always the third child of that particular generation.
This odd disorder was purely cosmetic, and William was otherwise perfectly healthy. William was a bookworm and very outgoing. Stanford startled William with accusations of being Bill Cipher in disguise. William laughed, as well as the rest of the family. It wasn't the first time. It was a bit of an inside joke that William might be a wizard blessed by their family's Guardian angel or something along those lines. He was brilliant and talented.
The family was tight-knit, apparently living on the same land for centuries. They were in the city of Rome, and some of the older family members spoke Latin as well as Italian and English. William and his siblings were still learning. Stanford warmed up to William, the two nerds bounding over a mutual love of knowledge. It was easy for William to understand Stanford's Unified Theory of Weirdness. Stanley was just glad to relax for a time. As it turned out, the Weirdness detected was sourced back to the oldest piece in their library, a painting of the family Guardian Angel, Will. Will was depicted as a Throne Angel with a triangle in the center of the wheels within wheels. It radiated Weirdness. According to the family, one of their ancestors, Daniel, had painted him in a fit of madness. The canvas was made from the skin of a dinosaur. The paint had a bit of the blood and bones of a Sasquatch. It gave the painting a strong contrast. William would sometimes stare at the painting whenever he had trouble sleeping at night. Stanley had to convince Stanford not to destroy the piece and, instead, take a video. However, the video was different from the painting; the wheels were very subtly moving in the image taken. The family was shocked to see this, but it only made them more attached to it.
The twins were at a loss; their mission was to cleanse the world of the Weirdness left behind by Bill Cipher. But this Weirdness seemed to be beneficial. The twins decided to keep tabs on it for the time being. They were leaving when William asked to return to America with the twins. Stanley liked the idea. Even though Stanford was on friendly terms with the boy, he felt it was a bad idea. He was willing to accept the kid's unusual disorder, but he was sure the rest of Gravity Falls would tear the poor guy to shreds. Stanley reassured him that William was his person, and as long as they made that clear, there shouldn't be a problem. William tagged along on the last leg of their journey and inevitably gained the nickname, Wizard Bill. William had learned some sleight of hand from Stanley and the chemistry knowledge from his time at home.
Wizard Bill and the Pines twins came back to America. The young man did what he could to be independent from the twins after he passed customs. The townsfolk of Gravity Falls ended up welcoming the twins and Wizard Bill with open arms. This surprised Stanford, and the twins discussed this in private.
"I don't get it," Stanford said, "Shouldn't the town be more hesitant to welcome this guy?"
Stanley asked, "Are you sure you're not still suspicious that Wizard Bill is Bill Cipher in disguise?"
Stanford sighed, "I'm sorry, Stanley, I can't help it. I've already misplaced my trust once with Bill Cipher. I don't want to end up doing that again."
Stanley chuckled, "After all this time, you're still paranoid."
Stanford sighed tiredly.
"Look," Stanley said, "I get it. This guy messed with your head, and now you have trust issues. Maybe you should try telling yourselves a simple phrase to remind you there's nothing to worry about anymore."
Stanford asked, "Like a mantra?"
Stanley nodded and instructed, "Repeat after me. Bill Cipher is dead, and he can't hurt me or my loved ones anymore."
Stanford repeated, "Bill Cipher is dead, and he can't hurt me or my loved ones anymore."
Stanley smiled and said, "If you feel yourself slipping into paranoia, just repeat that phrase. Because it's the truth."
Stanford murmured the phrase a few more times before taking a deep breath.
"Thanks," Stanford said with a smile, "Stanley."
Stanley said, "No problem, brother."
Wizard Bill was exploring the woods when he stumbled across it—Bill Cipher's old body. He immediately told the twins, and Stanley brought a sledgehammer. The Pine twins followed Wizard Bill. The statue had a bit of moss on it now, but it was otherwise unchanged. Wizard Bill noted that Bill Cipher's presence felt very different from the painting of Will. Stanley handed Stanford the sledgehammer.
"You should take first to whack," Stanley said, "He hurt you the most after all."
Stanford hit the statue as hard as he could with the sledgehammer. As soon as it made contact with the statue's eye, there was a loud BONG!
Wizard Bill fell to his knees, screaming in agony. He doubled over, holding his sides; a tinge of blood was in his tears as he wept in sorrow.
"Wha-" Stanford said as he immediately dropped the sledgehammer. Stanley was already at Wizard Bill's side.
Wizard Bill whined, "I don't understand why it didn't work. Why am I still connected?"
Stanley softly reassured, "Don't be so hard on yourself. You did what you could."
Stanford was very cross when he heard this. So Wizard Bill and Stanley went back inside the Mystery Shack with Stanford. They all sat down at the table to explain.
Stanford asked, "Something you want to tell me, you two?"
"I'll start," Stanley said and then told the story, "Bill had been a part of my dreams for a while after my memories finally returned. He was always on the edge, just watching. I approached him at first, very hostile and angry. Bill and I started fighting, but after a while, we started talking through our differences. He was insulted at first that I would even think to empathize with him. Then, I challenged him to use his power to try to live a human life. To see things from another perspective."
Wizard Bill said, "I took that Challenge and then some. So far, I have lived 333 human lifetimes, creating more than I ever thought possible. I made friends, laid the groundwork for multiple families, and gained an appreciation for this world. I admit I was to try to help my past self be stronger, but at one point, I became a mother. And when my old self demanded, I would sacrifice my baby. I refused because I loved that little boy. It was the first time I was protective of humanity. It wouldn't be the last. There was a bond there that seemed to transcend conventional reason. It was like Familial Love was the equal but opposite of my Weirdness."
Stanley explained, "He's been much better at empathy ever since, but today showed that despite everything, his power is still corrupted."
Wizard Bill said, "Stanford, you have to understand Bill Cipher is dead. Whatever small part of him you think is still within me or Stanley, try to picture it as a rotting corpse. Because that's all he'll be now."
Stanford let it all sink in, thinking it over. He took a deep breath.
"If what you're saying is true," Sanford told Wizard Bill, "Then you have already proven yourself to be very human. However, I do think in the present time, we should look into controlling the power within you for the greater good."
Wizard Bill said sheepishly, "My magic is much weaker than before, even within Gravity Falls. I don't have the same power I used to."
Stanley reassured, "Don't sweat it, kiddo, you're still so young. I bet that with time, you'll unlock more of the power you lost."
"Thanks, Stanley," Wizard Bill said.
Quietly, Stanford had felt that Bill hadn't changed, but he didn't have time to dwell on it as Dipper and Mable arrived.