Here, you thirsty little bitches (no offence, don't hurt me).
It's hard being what he is. He never asked for it. Never wanted it. He always hoped that he'd be able to live a moderately normal and successful life. However, that was all taken away from him when his sister made (another) bad (and devastating) life choice.
Just like that time she didn't tell Gideon 'no'; Just like that time she ran off with the Rift, playing a major part in the start of Weirdmaggedon, Mabel Pines did something terribly stupid. And, as always, she never apologized for it. Well, how could she this time? Dipper had killed her.
It was an accident. One he regretted deeply. He just couldn't get the images out of his head (unless he was in another rage). These are the consequences of being a horrid beast meant to kill and eat the flesh of its victims— no matter how close they were to you.
Mabel was unaffected by the curse, as was not the demon-turned-human, Bill Cipher. Why? They were both the cause. They found something that they shouldn't have messed with. Yet they did. Mabel took it home; Of course, after Bill urging her to. When the townspeople woke up the next morning, everyone except to two harbingers of the cursed object were turned into many forms of beasts. Most weren't too dangerous, with the exceptions being Wendy (the werewolf who couldn't control herself), Gideon (the mentally unstable vampire), Waddles (the massive boar monster), and... Dipper. The unpredictable wendigo now.
Why he did it didn't seem like a valid question to him. He didn't do it for a reason. Hell, he didn't even mean to do it. He wasn't in control of himself. Yet, people kept throwing that question at him. Shaming him. Calling him a monster— unsafe. He was locked in the basement, only able to see the people who occasionally came down with all sorts of weapons, bombarding him with more questions. Only one of his visitors didn't speak; Didn't brandish a weapon and wave it around in front of them, eyes wide as though he attacked them.
Bill just stared. Stood in the opposing corner and simply... stared at him. Watching him; Observed him. As the blond continued to stop by and just stare, Dipper contemplating killing him too. After killing his sister, he snapped back into reality only after he ate a large portion of her flesh off the bones. It left him with a strange, gaping hole in his stomach. As he ate, he only became more hungry. To say it was painful was an understatement. To constantly be hungry, only to grow hungrier with every bite you take, every chewed morsel swallowed? It hurt, not just physically. Dipper was close to losing it. He couldn't eat, yet he needed to. His conscience told him not to eat, yet with his decaying state of mind, his fading sanity... He didn't have the sense to listen.
Bill seemed to sense Dipper's increasing hunger. Whether it was the tongue swiping across his upper lip, or to predatory gaze that bore into his soul, he noticed like a sign was taped to Dipper's face that read: "I WANT TO EAT YOU". Bill was aware of the teens predicament, his struggled to remain lying there, his effort to keep his hunger under restraint. Finally, the wendigo shifted. He was sitting up now, glowering at Bill. It was like he was saying, "You're really testing me, bitch." Bill smirked and took a few steps forward. The brunet dropped the murderous look on his face, instead wiping off any trace of emotion, staring intensely at him as he walked halfway across the room. When he stopped, Dipper shifted again, licking his upper lip in anticipation. He was hungry and losing his sanity, which was evident in his body language. As blank as his face and eyes were, his posture, his occasional movements, they spoke for those missing giveaways.
Bill took a pocketknife out from behind him. Dipper glanced at it, evidently uninterested in the small weapon. It wouldn't do any significant damage against a creature such as him. He knew it, so he decided to ignore the "threat" altogether, as it was too small to inflict any real damage against him.