I spent a little more time on this one trying to get a satisfying conclusion. This will be in two parts, and then there will be an epilogue. Share you thoughts.
Stan squirmed and twisted, and out of his body emerged Bill Cipher, in physical form. He floated in front of Dipper, laughing maniacally.
"Ah finally! Weirdmageddon is back, baby! Worldwide Weirdmageddon for the win!" Bill did a little flip in the air.
Stan woke up.
"Gah, what happened?" He looked up. "You! Why I outta..."
"Stan, we gotta go! Now!"
Dipper grabbed Stan, who was still recovering from the possession. How did he get in my head like that? Wait...he used my grief for my brother against me...that's low, even for Bill...
Dipper opened the door to the car and helped him in as Bill grew 2 stories high, demolishing the hotel in the process, unleashing monsters from the portal. Dipper hopped in and Mrs. Boonchuy stepped on it. Stan sat next to Ford.
"Ford?"
"Hey Stan..."
"No...this has to be a dream..."
"I'm...not your Ford..."
"What? Then whose Ford are you?"
"I came here from a dimension that fell under Bill Cipher..."
"So, you didn't die in that reality?"
"No, but...everyone else did..."
"Wait, we gotta get my mom!" Luz said.
"Yea, she's no doubt in danger!" Amity said.
"We can't make too many detours," Ford said. "You're gonna have to call her and tell her to hide."
Luz sighed and called her mom. The phone kept ringing.
"Come on, pick up!"
Eventually, Camila picked up.
"Luz? How late is it? Why aren't you home yet?"
"We got a bigger problem!"
"Where are you?"
"We're being chased by a triangle demon, and you need to hide! Now!"
Camila heard a sound outside. It sounded like a giant's footsteps. She looked out the window and saw a car being chased by a giant triangle.
"I think I just saw it..."
"Mom, find a place to hide, far away from here!"
Camila immediately ran to the car. She started it up and drove towards the direction the car and Bill went. She had an idea.
Bill chased Mrs. Boonchuy's car downtown, smashing into buildings. The monsters from the Mindscape were causing pandemonium in the streets. Several cars crashed into each other as chaos unfolded. Camila couldn't follow them on that road, but she took a detour that could still lead to them. She could still hear stomping in the distance. She stepped on the gas, hoping to be able to catch up with them.
"He's gaining on us!" Dipper said in a state of panic.
Amity looked back at Bill...and noticed blue and green lights following behind him.
"Anne and Marcy are here!"
"Go for the eye!" Marcy said. "I think that's his weak point!"
"Got it!" Anne dashed in front of Bill and launched herself towards him. She punched through his eye, the shockwaves from her fist destroying it.
"Ahhh, you little! Gah!"
"I think they just bought us some time," Dipper said. "It will grow back so we need to be far away when that happens..."
Luz noticed a car pull up by them. Someone stepped out. No...
"Mom, I told you to find somewhere to hide!"
"I brought your portal..." Camila handed the portal to Luz. Camila turned to face Bill.
"Wait...mom..."
"Luz...you need to go with them..."
"No...mom...please..."
Camila turned her head to Luz.
"I love you, mija..."
Camila walked toward Bill. Luz rushed to try and get her back but Amity held her back.
"Amity? What are you doing?"
"Luz, listen to me...I think there's more to your mom than meets the eye..."
Wait...what is Amity implying?
Bill reformed his eye and looked at Camila.
"Ah, aren't you a brave one?" Bill mockingly said. "Or maybe a foolish one..."
He swung his arm down at her to crush her in an explosion of asphalt.
"Mom!"
Luz fell to her knees in tears...why did you have to do that?
"Heh, what a shame..." Bill chuckled.
He lifted his arm, only to notice that she wasn't there.
"What?"
Camila appeared behind him, holding a staff. She blasted Bill in the back, causing him to fall forward.
"Gah, what the hell?" Bill was shaken, but managed to get back up and face Camila.
Did...did my mom just...do magic?
Camila revealed her real ears...
"My mom is a witch?"
"That's...Azura's staff!" Amity said.
Does that mean...my mom...is Azura?
Camila turned to face Luz.
"I'm sorry, Luz..."
Camila readied her staff to do battle with Bill Cipher. Anne, Sasha and Marcy stood alongside her.
"This is starting to get irritating..." Bill started to turn red from anger.
"I think we need to go," Ford said.
"But my mom..."
"I think your mom has this handled. We need to have a plan."
Luz reluctantly went with the others.
I hope you're right, Ford...
"Hey guys," Dipper said to Anne, Sasha and Marcy. "You're gonna need this." He tossed the Calamity Box to Anne.