Remix version of Sonic and Metal:

https://youtu.be/Hpxy7ATsBmY

The factory made it's way to the city in San Francisco where Sonic and Dr. Robotnik last fought before transporting one world to another. There were people in the city that didn't expect to see the factory standing above them like a gigantic robot ready to tear down the city. 

"HOHO! Isn't it glorious to be back home?" Dr. Robotnik cackled.

"You won't get away with this." Tails remarked.

"I've already had once Sonic is finished for good." Dr. Robotnik smirked.

"What the heck is power this thing?" Chi-Sun asked.

"In case you haven't figured it out already. I asked Shadow to find me the chaos emeralds to help me upgrade this thing. It still has a lot of power inside of its battery but it also helps it charge it up rest." 

"That explains why he used them to spawn the portal back to earth," Bethany said.

"We need to get the chaos emeralds out of there now!" Chi-Sun said.

She was about to run behind Dr. Robotnik's back when Shadow cut right in front of her square punching Chi-Sun in the face. The others were shocked when Chi-Sun held her cheek and glared at Shadow who stood there emotionless.

"Move out of the way Shadow! I need to get those emeralds and if I don't then things will only get worse." Chi-Sun gritted her teeth as Shadow stood there staring at her with the same frown.

"I can't allow you to go past the doctor. It's his order to keep anyone from getting near the emeralds." He replied as Chi-Sun growled in return while you were on the floor crying to death about learning what happened to your family.

Outside of the factory that turned into a giant robot Sonic and Metal Sonic were still fighting. This made Sonic more frustrated by the fact that Dr. Robotnik had programmed Metal Sonic to keep up with the pace as he and they are running around the city chasing each other.

"Geez, Dr. Robotnik made sure that you can keep up with me alright." Sonic grinned.

"Let's see how fast can you go." 

The faster Sonic went so did Metal as he followed Sonic around the city to try to get him away so he can head back where the other's were held captive by the evil scientist. Sonic looked around the area to get Metal to stop chasing him as he spotted a gas truck riding around he ducked under it but Metal copied him. This gave Sonic the chance to dip him into running into a building that shocked everyone to run away from the scene.

"That'll buy me some time to head back to the other's," Sonic said.

He raced back to the factory while Metal Sonic began to act much differently in the calculations that cause him to spaz out a little his that started to construct him. 

Sonic

I made it back to where the other's were and saw Y/N was passed out on the floor, Chi-Sun was arguing with Shadow that only left Tails and Bethany trying to figure something out.

"Sonic! How did you manage to beat Metal Sonic?" Dr. Robotnik asked.

"I didn't. I left him to crash in the wall so I can come back here." I replied as I felt a shiver as I held myself and looked back at Dr. Robotnik. "Yo Robotnik, why is it so chilly in here?" 

"S-Sonic...He-He..." I heard my poor and sweet Y/N quivering through her words as I rushed over to her taking Y/N away from Robotnik. "Y/N what happened?"

"H-He killed them...he killed them..." She cried.

I was confused about what she was referring to and asked, "He killed who?" 

"Sonic...Dr. Robotnik killed Y/N's parents." Tails spoke up.

My mouth dropped as I heard the horrible news coming from him because I remember Y/N telling me she lost her biological parents and Tom's parents adopted her into the family.

"No..." I mumbled as I glared over at Dr. Robotnik who grinned.

"How touching to see you two talk about life and death of a loss. The next phase is to hold each and one of you captive to watch the screen as the destruction of this city get torn down." He cackled.

"Sonic...please stop him! He's going to kill all of us if we don't-" Bethany was cut off when I heard Y/N scream as she was held in a robot's grip in pain. Her eyes were the color purple changing to gold again as she tries to hold back the tears coming down her face. 

"Y/N!" Bethany shouted as she tries to run over to her friend when Robotnik did a move to knock her unconscious and Tails ran over to her only to get kicked by him.

Dark Sonic Scene:

https://youtu.be/tiAFyEbdjF8

"Now Sonic, prepare to be crushed by my next two creations I made to annihilate you." Dr. Robotnik snapped to summon two taller robots that walked over to me ready to take me down.

I collapse onto my knees blocking everything out except seeing Y/N's face made me feel...different inside. 

"I-I never saw Y/N look so scared," I said.

"She should be because what other option was I suppose to do to make it feel less entertaining?" He chuckled.

I felt dark aura form around me as my fur changed black and my eyes remained the same as my voice changed more assertive and aggressive, "And-And Bethany you knocked her right out. Why did you that?" 

"She had to be stopped there is no point in protecting that girl. She's already been a freaked from the beginning and these people shouldn't be helping her in this situation." 

I felt a pang through my chest listening to him taunting about them making me so angry as I formed a fist and chuckled darkly, "Oh, alright then, let's test them out!" 

I charged straight over to the first two robots taking them down so fast and then took down the one holding Y/N as I held her in my arms protectively and triumphed with a dark smile.

"Hehe, it looks like you have to go back to the drawing board~" I smirked.

"Settle down Sonic. This isn't like you at all and I never saw you worked up before." I heard Tom as I realized that I was scaring everyone by my actions as I calmed myself down to return normal.

"I-I'm sorry guys." I apologized.

"It's fine. For now on, don't take your anger too seriously." Knuckles said.

"Any idea if you guys have seen Dr. Robotnik just now?" Tails spoke up.

"He's gone!" Maddie explained.

"All right, everyone we need to get out of here. Tom, I need you to take Y/N somewhere safer and the other's too." I said as he nodded taking Y/N out of my arms.

"What about you Sonic?" Lizzie asked.

"I'm gonna take care of Dr. Robotnik." 

"How can you when he's using the chaos emeralds that are in the control room? Shadow won't let me get past him." Chi-Sun said.

"Shadow please we need them more than anything." Tails begged.

"I'm not letting you get past me. Take another step and I'll swipe you away." He warned.

I was about to get up but Chi-Sun prevented me to go up to him and she said, "Shadow...we're here to stop Dr. Robotnik from destruction and whatever is causing you to do this. It needs to stop. Look, I'm not a good person when it comes to words, but what I'm saying to you is...please be a friend and help us out." 

Shadow was about to respond when Chi-Sun bent down his level hugging him as his eyes widen. But I can tell he was fighting back some tears that only meant that someone he met that reminded him so much that resembled Chi-Sun. 

"...Fine. I'll help you all." He said.

"Thank you, Shadow." She nodded.

"All right, follow me to the exit while Shadow and Chi-Sun get the emeralds," Tom said.

"We'll be right behind you guys!" Chi-Sun said running behind Shadow to get the emeralds while I ran the other way to find Dr. Robotnik and defeat him for our last fight.