It wasn't unreasonable for Dipper to assume he was dreaming. Bill was just messing with him. Or maybe it wasn't Bill at all; maybe he'd become so paranoid about going to sleep that his mind was starting to play tricks on him (besides, the figure outside the window certainly didn't look like Bill). The being's golden triangular form had been replaced with a human one - the same human Dipper had conjured up on paper just a few hours beforehand. He studied the being carefully, drawing connections between the demon and the character he'd drawn in his mind. There was the top hat, the bowtie, the colours he'd been forced to use on his drawing due to Mabel's lack of consideration for his stationary. Possibly the most prominent similarity between the two was the fact that only one of the being's golden eyes was showing (the other was covered by an eyepatch which was in turn partially hidden behind a mess of golden hair).
By this point Dipper had arrived at the conclusion that in his sleep deprived state, he was being deceived by his own mind and attempted to prove this to himself by checking the sketchbook he'd left on the desk across the room. If the drawing was still there, he decided, then his mind was playing tricks on him. Trouble was, the drawing wasn't there. It had disappeared from the page completely, except the mark his pencil had left in the bottom right-hand corner of the page remained. For a moment, he refused to believe it.
"I'm right here, Pine Tree. All you have to do is let me in." The familiar sound of Bill's voice distracted him from his thoughts and confusion, and his attention immediately gravitated towards the being outside the window. Their eyes met and a shudder ran down his spine. Without a word, he turned away and walked towards the door, heading downstairs. He passed Grunkle Stan on the stairs but was concentrating far too much on the alleged demon floating outside the attic window to notice anything else. By the time he reached the front door and pulled it open, Bill - if it really was him - was already waiting for him outside.
Running his fingers through his hair, the demon stepped inside - pushing the human away in process - and flashed a knowing grin in his direction. "I knew you wouldn't let me down, kid," he beamed, his one visible eye glistening. As he stepped further into the Mystery Shack, the door closed itself behind him - as if by magic. He glanced around the hallway for no more than a moment, and then grabbed Dipper by the wrist and dragged him back up to the attic, knowing no-one else would be there.
Dipper considered the repeated use of that god forsaken nickname - "Pine Tree" - as confirmation of the being's identity. Before he could ask what he was doing there, Bill interrupted his thoughts yet again with a maniacal chuckle. "You really don't want to believe it's me, do you?" he laughed, a golden cane suddenly materialising in his hand which he then used to push the human back onto his bed. The cane vanished from his hand then, leaving no evidence of its existence behind.
Dipper shook his head and scrambled away from him, backing up against the wall even though the demon hadn't moved an inch. "What are you doing here? And why aren't you in your normal form?!" Bill's visible eye twitched slightly in reply and he put one finger to his lips, silently telling him to keep quiet. The two of them could hear somebody moving about outside the door. Footsteps echoed off the walls in the hallway, louder when they were closer to the door, but faded quickly without disturbing them too much.
"Oh, you know, just fancied a change for once. Good job on this, by the way. It's not bad at all." He kept his voice surprising low, presumably to avoid anyone overhearing him. "I'm not here just to hang out with you, kid. We need each other… besides, I owe you for this." He gestured to himself before returning his gaze to meet with Dipper's and approaching the human ever so slightly, taking one or two steps closer to the bed. Dipper grimaced in response and instead of getting even closer to him, the demon crossed the room to sit in the chair by the desk on which he had found his new body. "We both know you can't win that art competition on your own, Pine Tree. You might like to think that you can and, admittedly you did do a remarkable job on this, but the fact is you need me. Let me be your… inspiration."
"I'm not making any deals with you, Cipher," Dipper growled through gritted teeth. Regardless of the demon's new appearance, he was still Bill Cipher. He was still lethal, still corrupt.
Bill cocked his head onto one side, smirking, but stayed silent. "Alright," he said after a moment of sitting in deep thought. "No deals. But I still owe you for this, so I'm going to help you out anyway." Dipper's mouth fell open in shock but no words could struggle their way out. Based on his previous encounters with Bill, the words "kind" or "generous" were the last ones he'd use to describe the demon and yet, here he was, offering to help him expecting nothing in return. "Don't look so surprised, kid. I'm not all bad." Dipper raised an eyebrow at this statement but soon found himself resigned to the idea of accepting Bill's help - though he remained opposed to officially making a deal with him.
Footsteps interrupted them once again, this time failing to go away quickly. When the door was thrown open and Mabel skipped in, pausing when her eyes landed on a stranger sitting in their desk chair, Dipper suddenly became alarmed and threw himself off the bed whilst the demon remained relaxed and nonchalant. She turned to her brother, who hastily clambered to his feet and stood in between her and Bill and took an almost protective stance. Gesturing to the tall blond stranger in the corner of the room, Mabel asked him (in an annoyingly giggly voice) who it was and - as always - Bill refused to let Dipper speak first.
"The name's Bill. I'm P- er, I'm Dipper's friend." Dipper opened his mouth to protest, but the demon rose from his seat, moving to stand next to him, draped his arm over the human's shoulders and pushed the human's upwards, closing his mouth for him. "Oh, and he's invited me to stay for a while. I hope that's okay with you?"
Completely taken in by the demon's façade, Mabel's face broke into a wide grin and she nodded eagerly, glad that her brother had seemed to find a friend. Up until this point, he'd been spending time with Wendy and Soos but she really thought he needed to find some friends of his own age. The fact that her brother had never mentioned his supposed friend - along with how unlikely it was that Grunkle Stan had given his permission for someone else to stay with them, and the remarkable number of striking similarities between this Bill and the dream demon of the same name - seemed to fly right over her head. Dipper shot her warning look but she failed to notice this as well.
"Well, I'd better be going," she grinned, picking up her backpack from the floor by her bed and turning to face the door. "We're all going to out to find some more inspiration. See you later!" ("We" in this case probably meant her, Candy and Grenda, seeing as she'd joined their team for the competition following her argument with Dipper.) Slinging the backpack over her shoulder, she bounded out of the room excitedly, leaving her brother frowning after her.
The sudden change in her disposition was unnerving - though Bill had the same unsettling ability. She'd been uncharacteristically cold towards him the night before during their heated argument - a drastic change from her usual cheerful and eccentric temperament - and yet now she seemed to be back to her normal self. As Bill pointed out to him after she left, this was probably just a front. She hadn't forgiven him yet; she was merely pretending she had, possibly to make him feel guilty. According to Bill, this was why he needed him.
He couldn't do it on his own, the demon told him. She'd beat him and make him look like a fool. But if the two of them worked together on it, they could accomplish anything. Maybe he was right.
Pushing any and all thoughts of the journal's warning out of his mind, Dipper closed his eyes and took a deep breath, trying to prepare himself for what he was about to do. "Fine, you can help me. I'm not making any deals with you, but I'll let you help me."
His better judgement was still nagging at him, telling him ignoring the warnings was a bad idea.