It's a beautiful day on the planet Earth S. More specifically, in an area called Green Hill. It's got palm trees, variant fauna and flora, waterfalls, and luscious grassy hills. Most of those who lived on the planet were enjoying it. However, there was someone who wasn't outside enjoying the day. A mad scientist with a 300 IQ who goes by the name Dr. Eggman (though he used to be called Dr. Ivo Robotnik). He's currently in his base located far from the green hills of Mobius. Dr. Eggman has always tried to achieve his ultimate goal of expanding his Eggman Empire. He tries to do this by making badniks powered by little critters (they'll be called Flickies for the remainder of the story) and other strong robots. Despite how close he's come to achieving total victory, he's always been stopped by a group of anthropomorphic creatures, mostly a blue hedgehog named of Sonic.

Sonic holds the title of fastest thing alive. Not only can he go faster than the speed of sound, he can also run at light speed (even surpassing that on occasions). Ever since the speedy hedgehog and evil genius first met, Sonic had made it his mission to stop Eggman's evil plans. Over the years, the blue hedgehog has made many friends. He met a two tailed fox named Miles Prowler (but everyone who knows him just calls him Tails). He's pretty much Sonic's right hand man (well fox in this case). Tails also happens to have an IQ of 300 despite how young he is. There's also a red echidna named Knuckles. He's the last of his kind who guards the master emerald, a powerful gem that can control seven other gems called the Chaos Emeralds (more on all of them later in the story). The echidna was tricked by Eggman into thinking that Sonic and Tails wanted to steal the master emerald. Knuckles believed him and didn't realize that he had been tricked until the scientist had taken the powerful gem from an old echidna temple known as Hidden Palace Zone. The three of them are now allies today who all try to stop Eggman, though the blue hedgehog and red echidna still bicker from time to time. The last of his closet friends is a hedgehog like Sonic, except she's pink. Her name is Amy Rose. They first met on Little Planet, a place that only appeared once a year. She was captured by Metal Sonic, one of Sonic's robotic counterparts. Soon after Amy first met Sonic, she developed a huge crush on him. She's tried hard to win Sonic's heart, but Sonic never shared the same feelings. Amy has toned down her obsession with the blue blur over the years, per request of Sonic and their other friends, though she still has feelings for him. Despite how she tends to be around him, Sonic is glad to have Amy as one of his friends.

In Dr. Eggman's Base:
For the past few months, the evil genius had been doing research on another dimension called Equestria. He's also been gathering the seven chaos emeralds in secret so that only he and his minions are aware of his plans.

"Cubot, what's the status? Do we have all of them?" Eggman asked the yellow and black robot with a cubic face, chest, and lower body.

"All of what, exactly?" Cubot asked his master.

"Grr, the CHAOS EMERALDS! DO WE HAVE ALL OF THE CHAOS EMERALDS?" Eggman angrily answered.

"Oh those, my bad" Cubot sheepishly said. "Orbot should be back with the seventh one soon."

"How soon?" The scientist asked him.

"How about right now?" a red robot with a half spherical face and lower body said as he entered the base's computer room.

"Orbot, you're back! It was getting boring around here without you to talk to," Cubot said as he went over and hugged his robot friend.

"So did you get the chaos emerald?" Eggman asked Orbot. Orbot then opened his mouth to reveal the emerald.

"You did it, you actually did it!" Eggman said with excitement. "Hold on, didn't I send some egg pawns and other badniks with you?" The scientist then questioned.

"Um, about that, not long after we entered the area containing the emerald, Knuckles dropped down from the ceiling. All of the badniks then went into a fighting stance and starting attacking him. Knuckles then started to fight back. As you can probably tell, most of them didn't make it," Orbot sheepishly answered.

"How many of them actually survived?" Eggman asked with a stern tone.

"How many did you send again?" Orbot asked nervously.

"I sent 11 egg pawns, 3 moto bugs, and 3 blue bombers to help you," Eggman answered. "Don't tell me that you lied and all of the egg pawns and other badniks that I sent are reduced to scrap," he said with a rise of aggression in his tone.

"You can come out now X," Orbot said towards the door to the right of Eggman's computer.

"Uhh, who's X?" Cubot asked. An egg pawn then came into the computer room while walking slowly towards Eggman.

"This is X," Orbot told Cubot and his boss. "He found the chaos emerald while most of the other badniks you sent were fighting Knuckles."

"Is this true?" Eggman asked the orange robot. The egg pawn quickly nodded in response.

Cubot then noticed the letter X was written on the egg pawn. "Why is the letter X on the robot?" He asked his friend. Eggman then also noticed the letter on the lone egg pawn.

"I just happened to have a marker with me, so I decided to label him after he managed to find the last chaos emerald so I would remember which of the egg pawns found it since you make so many of them with no differences," Orbot answered his boss.

"I'm not even going to ask why you kept a marker with you," the scientist said to the red robot with a bit of concern. Orbot then handed the chaos emerald to Eggman. The scientist then opened a special briefcase with his face on it. It contained the other six chaos emeralds that he'd spent months gathering in secret.

"Finally, I've got ALL the chaos emeralds!" Eggman said with excitement. He then looked over at Orbot, Cubot, and the lone egg pawn and gave them a grin.

"I must admit, I'm impressed that neither of you managed to royally screw up this plan," he said speaking to Orbot and Cubot. The two robots gasped, not used to their master giving them a compliment or any sort of praise.

"Are you giving us praise for what we did?" Orbot asked with shock in his voice.

"Yes, I am," Eggman responded. Orbot and Cubot started cheering and dancing in excitement. "Don't get used to it you two," Eggman said interrupting the two.

"We won't, we're just happy we got it at all," Orbot said calmly in response. "So now that we have all of them, what's next in your plan?" The red robot asked.

"I'll explain that later. For now, we move on to phase 2 of the plan," Eggman replied as he put the last chaos emerald in the suitcase before closing it.

"What's this plan called anyway?" Cubot asked.

"It's simply called Interdimensional Takeover," the scientist said with an evil grin on his face. He then commanded the two minions (and X) to gather troops and head for the forest.

"Yes sir," Orbot and Cubot said while the two and the egg pawn saluted him. After the three robo minions left the computer room, Eggman grabbed a remote lying around and pushed a blue button. A closet door opened containing three robots: a grey one, a blue and light blue one, and a mostly regular blue one. All three resemble Sonic the Hedgehog, Eggman's greatest foe, to at least a small extent. The grey one is called Robo Sonic. The blue and light blue one is called Mecha Sonic. The mostly blue one goes by the name Metal Sonic, a literal metal copy of the blue blur.

"Robo, Mecha, and Metal Sonic, follow me! We're heading to Forest Hill!" Eggman commanded the three bots. After putting the remote in his suitcase with the emeralds, he closed the suitcase, and the four exited the computer room.

(End music)

On Angel Island:
Knuckles the Echidna was sitting on Angel Island guarding the Master Emerald like he usually does. While admiring the birds flying in the sky, the giant emerald starts glowing and making noises. Knuckles goes towards the emerald to see what the problem is.

"What's going on? Are the emeralds in danger?" The echidna asked. He was then showed all seven emeralds in one place heading towards the forest. Knuckles didn't think that Sonic or Tails had them. He then thought of Shadow and Eggman, but wasn't entirely sure if it was one, the other, or both. He then decided to go look for the blue hedgehog and yellow fox to see what they think. The red echidna then proceeded to glide off of the island towards his friends.

At Tails' Workshop:

Sonic was eating some toast and listening to some music with headphones on while his best friend Tails worked on upgrading one of his gadgets. While jamming out, Sonic noticed Knuckles gliding towards the garage door. The hedgehog then put his headphones down and went towards the door to greet his friends.

"Hey Knuckles. What's up?" Sonic said to the echidna.

"The Master Emerald is what's up," Knuckles said the hedgehog.

Tails stopped what he was doing and proceeded to ask "Did the Master Emerald get stolen again?"

Knuckles looked at his friends giving him annoyed looks and responded "That Master Emerald is still on Angel Island. It's what I was shown by the emerald that brought me here."

The hedgehog and fox looked at each other with a concerned look on their faces.

"So what did you see?" Sonic asked.

"I saw the seven chaos emeralds together, all in one place, heading towards Forest Hill," Knuckles had answered.

"All seven of them in one place? That means someone else has them," Tails responded.

"That's what I thought too," the echidna said. "Then I came here, I figured either Shadow or Eggman had all of them."

Almost immediately after Knuckles finished his sentence, a black and red hedgehog warped into Tails' Workshop, startling the everyone else inside.

"Speaking of Shadow," Sonic said right after the hedgehog had appeared in front of them.

Shadow, AKA the Ultimate Life Form, was a hedgehog just like Sonic. While Shadow was fast like Sonic, the two were different in nearly every other category. Ever since Maria, his best friend, was killed in an incident on a space station called Space Colony Ark, he tends to do things by himself. He has helped save the planet a few times, and he's appreciated for it. Sonic and his friends also respect Shadow's personality and don't bother him unless they need him. So while the two hedgehogs aren't enemies, they aren't necessarily friends either (friendly rivals is the accurate term).

"I just spotted something in the forest," Shadow told the group.

The group was still a bit startled by Shadow's sudden appearance, but Knuckles was still able to say "I guess you don't have the chaos emeralds after all."

"And why would I have them?" Shadow asked a bit offended.

"Don't worry about it Shadow," Tails said to the black hedgehog. "What did you did you see?"

"I saw the doctor with a briefcase, and his minions in the forest," he answered.

"How many minions did he have? Was it only a handful?" Sonic asked.

"A lot more than a single handful," Shadow answered.

"That's not a good sign," Sonic replied. "And he has a special briefcase? We need to find out what the egghead is up to."

"Agreed. I'll go after myself. You three can join me if you want to," Shadow said before dashing towards the forest.

"Let's have some gear on us. Just in case," Tails said to his friends.

"I'm with you on that buddy," Sonic responded. "Him with tough robots on his side is one thing, but that briefcase could have something in there that could spell bad news for us."

"I'll meet you guys there. I have to check something back on Angel Island," Knuckles told Sonic and Tails.

"Okay Knux, just don't take too long," Sonic told him.

"I don't plan on it," the red echidna replied before running towards his island.

Sonic and Tails then grabbed some equipment. Sonic grabbed a bracelet that would allow him to bounce with increasing heights and a gold ring with a crystal the shape of a raindrop on it but is a shade of red instead of blue. He also picked up a light blue ring, placed it in a special container, and placed that container in a bookbag. Tails opened a drawer containing what looked like mechanical boosters. It was his jet anklet, something that allowed him to fly faster than normal. Tails also grabbed a silver toolbox with his face on both sides of it.

"Hey Tails. You got everything you need?" Sonic asked while he was somewhat impatiently waiting by the garage door.

"Almost. Just need to grab a few more things before we head out," Tails told his best friend. After the fox and hedgehog grabbed everything they needed, the two sped towards Forest Hill.

Knuckles had just reached his island by the time Sonic and Tails had left. He made sure that the Master Emerald was protected just in case someone else tried to steal it and he grabbed some equipment of his own before leaping back off of the island to meet his friends and Shadow to find out what Eggman is up to.

Forest Hill was a more dense part of Green Hill. It contained beautiful floral, fauna, and plenty of trees and logs that were perfect for parkour. While Shadow was making his way through the forest to try and catch up with Eggman, he thought to himself "This reminds me a lot of Prison Island and Death Ruins." Despite the urgent matter, Shadow is still careful not to hurt any creatures living in or near Forest Hill. Not only did he have to be careful to not hurt and fauna, he also had to pay close attention to what was in front of him since there were a lot a leaves that temporarily blocked his vision.

"The doctor's got to be somewhere in this forest, I just know it," the black hedgehog said to himself. He eventually decided to pick up the pace and started to boost in order to find Eggman faster and get rid of any old logs in his path (don't worry, no creatures were harmed). After about 15 seconds of boosting and some more platforming, Shadow heard some machine like sounds and stopped in his tracks. The black hedgehog had reached his destination.

(End music)

Shadow found some bushes to hide behind to avoid being spotted. He saw Eggman, Orbot, Cubot, Metal Sonic, two other robotic Sonics, and a bunch of badniks created by Eggman. Some of them were egg pawns with rocket launchers. Despite the amount of robots with Eggman, Shadow's attention mostly focused on the robotic Sonics near Eggman.

"Wait just a minute, I thought there was only robotic version of Sonic. Why does it look like there are three of them?" Shadow asked himself. Not long after he asked, Sonic, Tails, and Knuckles showed up behind him.

"Hey there," Sonic said casually while Shadow gasped in surprise.

"Oh, it's only you," Shadow said after turning around to see who had appeared. "How did you three get here so quickly?"

"I've been through Forest Hill plenty of times. I know almost every part of it like the back of my hand," Sonic said confidently. "By the way Shadow, does this place remind you of Prison Island in any way?"

"As a matter of fact, it does," Shadow answered. "Why do you ask?"

"No special reason," the blue hedgehog replied. "Anyways, what did you find out?"

"Well I found out that Eggman has three robotic copies of you," Shadow answered. Sonic, Tails and Knuckles then looked to spot the three bots Shadow was referring to.

"Oh, them," Sonic said seriously while looking at Robo, Mecha, and Metal Sonic.

"Did he make those other two copies after making Metal?" Shadow asked Sonic.

"Actually, those other copies were made after Metal," Sonic said.

"When did you meet those other two?" Shadow then asked.

"After I trashed Metal for the first time, I fought Robo Sonic on Egghead's space base," Sonic recalled.

"I assume you're referring to the one that you were kept in for 6 months," Shadow replied.

"That's the one," Sonic said confirming Shadow's guess. "After that, Tails and I fought Mecha Sonic, that blue and light blue robot that tries to look like me."

"I later fought him myself, and he used the Master Emerald to try and beat me. Of course to no avail," Knuckles had said proudly.

"Of course the doctor made multiple robotic copies of his greatest rival," Shadow had replied.

"And of course all of them failed," Sonic said with a smirk.

"I suggest we all be quiet so we can see what Eggman is up to, and it will be more difficult if we're caught," Tails told Sonic, Knuckles, and Shadow in a whispering tone. All of them proceeded to cease talking while they spied on Eggman and his minions.

Eggman then opened a briefcase containing the chaos emeralds, a black sphere, and a remote. Sonic and crew looked at the scientist in shock.

"That's why the Master Emerald showed me all 7 chaos emeralds in one location moving at the same time! Eggman kept them in that suitcase!" Knuckles said quietly.

"I say we rush the doctor and take the emeralds back right now," Shadow said, knowing just much about what the emeralds are capable of as Sonic and Eggman.

"Easy there Shadow," Sonic said while trying to calm down the black hedgehog. "I'd normally do the same thing, but there are a few more things we have to factor."

"Like what?" Shadow asked.

"First off, the chaos emeralds can be unpredictable at times. They could go out of control if something goes wrong," Tails answered.

"Second, even if though we could probably take down those egg pawns and other badniks with ease, there are still the robotic copies of me that we'd have to deal with, and I doubt they'd just let us take the emeralds from Eggman," Sonic then reminded Shadow.

"As much as I hate to admit it, I think Sonic and Tails are right about this," Knuckles then said. They four then noticed Metal Sonic looking around and ducked before he could spit them.

"Fine, but just know that I'm not a fan of this," Shadow said with some annoyance in his voice.

"Wasn't expecting you to like this plan," Sonic replied.

Eggman then took out the remote and pressed a green button. That button caused the black sphere to turn into a machine that Sonic and crew had never seen. It looked like a giant black eye with a red eyeball. There were 7 holes around it, and the holes happened to be the same size and shape of the seven chaos emeralds. The heroes just watched from the bushes as Eggman was about to power his machine. Shadow didn't want to sit back any longer.

"Now do we intervene?" Shadow asked Sonic. Sonic then looked at Tails and Knuckles who both gave a smile and nod signaling that now they'd intervene and try to stop Eggman.

"Time to intervene," Sonic said with a grin on his face. The group then got out from the bushes and Sonic yelled "Hold it right there, Eggman!"

"Well, well, well. . . If it isn't Sonic, Tails, Knuckles, and Shadow!" Eggman said to the anthropomorphic creatures. "What can I do for you on this fine day?"

"How about you tell us what the deal is with that machine of yours?" Shadow asked.

"That isn't your concern, my dear Shadow," Eggman replied. He then sent his minions to keep Sonic and the others busy while he placed the chaos emeralds in his special machine.

"Is it robot trashing time?" Knuckles asked enthusiastically.

"It's robot trashing time," Sonic said eagerly.

Sonic, Tails, Knuckles, and Shadow then started to fight some of Eggman's badniks. Robo Sonic was about to go and join in until Eggman held it back.

"No. You three stay with me for the time being. I will let you know when it's your time to strike," Eggman told the robots.

"What about us?" Orbot asked.

"Do we stay back too?" Cubot followed up.

"Yes. You're not exactly capable fighters. Although I do have Robo, Mecha, and Metal Sonic, they're not as easy to build. There's also the fact that you two can talk but those three can't," Eggman told Orbot and Cubot.

"Well, at we have some reason to stick around," Cubot said optimistically.

"With that settled, let's finish phase one of my plan," Eggman said. He then instructed the 5 bots to take out a chaos emerald and place it in one of the holes. They all took one out and placed them into one of the holes on the side of the giant eye.

With Sonic, Tails, Knuckles, and Shadow

Egg pawns, moto bugs, and buzz bombers were swarming Sonic and crew. While they were easy to take down, the number of badniks kept them occupied. Some of the Egg Pawns even had lances to cause serious harm.

"We've got to get those emeralds back!" Knuckles said angrily while throwing one moto bug into an egg pawn, destroying both in the process.

"We need to clear out these badniks first. Otherwise, we won't be able to reach Eggman," Tails responded.

Sonic and Shadow were also contributing by using their homing attacks against the buzz bombers.

"Grr, how many more of these things are there?" Shadow asked.

"There can't be that many left," Sonic said in response. "At least they're easy to take out."

"True," Shadow said quietly in agreement.

"Sonic Wind!" Sonic said loudly while summoning a blue tornado.

"Chaos Spear!" Shadow said while throwing three energy spears at three egg pawns. The robots surrounding them were reduced to scrap metal within seconds. There weren't that many robots left, but they were buying Dr. Eggman the time he needed.

As he put the final two emeralds into the machine, the scientist had an evil grin on his face. The chaos emeralds then lit up as a sign that the machine was ready for use.

Sonic saw that the machine was ready and yelled out "We need to finish these guys NOW!" The anthropomorphic creatures then spin dashed to destroy the remaining badniks around them. They went towards Eggman, but Robo, Mecha, and Metal Sonic stood in their path.

Eggman was about to press the button on the remote that would activate the machine, but Shadow had other plans. As the robotic Sonics came and prepared to fight, Shadow charged a chaos spear and launched it at Eggman. He tried to hit his hand to knock the remote out of it, but the black hedgehog's aim was slightly off. Instead of hitting the doctor's hand, the spear hit the button that Eggman was about to press.

"Ahh, what did you do?" Eggman yelled as he dropped the remote.

"What exactly did you do?" Sonic asked Shadow.

"I was trying to knock the remote out of the doctor's hand, and I did," Shadow replied.

"You were aiming for the remote?" Sonic asked a bit confused.

"I was actually aiming for his hand," the black hedgehog answered.

"Normally, that would be an automatic win for us, but that machine contains the 7 chaos emeralds," Tails said with worry in his voice. After Sonic, Knuckles, and Shadow gave Tails a confused look, the fox pointed to the short circuiting remote.

"The remote stopped working. What's the big deal?" Sonic asked, still not knowing what the problem was. However, Knuckles figured it out almost immediately after Sonic asked his question.

"The chaos emeralds!" Knuckles said while pointing at the machine. Sonic, Tails and Shadow looked towards where Knuckles was pointing and saw the emeralds start to go out of control, which was affecting the machine as well.

"Uhh, what's happening to egghead's machine?" Sonic asked with a worried look on his face.

"When Shadow used his chaos spear, he didn't just hit the remote. He also hit the button that would have turned the machine on!" Eggman said while upset. Right after those words were said, the chaos emeralds had opened up a portal. However, due to the machine's malfunction, the portal had a strong pull that was almost impossible to resist.

"Orbot, what should we do?" Cubot asked his robot companion.

"Well I think we should all. . ." Orbot paused before yelling "RUNNNNN!" However, running was futile. The power of the emeralds made the portal super strong. Robo and Mecha Sonic were the first ones to go through. Eggman, Orbot, Cubot, and Metal Sonic tried to get away, but they were sucked into the portal as well.

While this was happening, Sonic, Tails, Knuckles, and Shadow were holding on to whatever they could, but their grips wouldn't last long.

"Sonic, what do we do?" Tails asked, struggling to maintain his grip on a nearby rock. Sonic wasn't to sure at first, but after seeing Eggman and his robot minions go through the portal, he had made up his mind.

"We're going through that portal!" Sonic exclaimed.

"What?! Are you crazy?" Knuckles yelled confused and thinking that this was a bad idea.

"We may not know where that portal leads, but I'm not going to let Eggman cause trouble wherever he ends up!" Sonic boldly stated. The blue hedgehog then let go of the tree he was holding on to and spin dashed towards the portal, eventually jumping in it.

"Sonic!" Tails screamed. He was about to lose his grip but Knuckles pulled his friend next to him.

"Let's go join him," Knuckles said before he grabbed the fox and ran into the portal.

Shadow simply said "Eh, why not?" He then spin dashed towards the portal and jumped in before it closed.

Author's Note

And that's chapter one of my new fan fiction. Sorry if some parts of this chapter are shorter or longer than others, but I'm not used to writing dialogue in a story. Heck, I'm not used to writing stories at all, so please cut me some slack. I do aim to improve as I write more of this crossover story.

This chapter was a simple introduction to the Sonic characters that'll be featured in this story, so I felt the need to explain some of the history between them.

In terms of Mobius, Green Hill, and Forest Hill, this was one of the hardest things to try to explain in this chapter. For this story, Green Hill and Forest Hill are both parts of Mobius, but the environments are different.

Now for some references/callbacks:
Eggman saying "Finally I've got ALL the chaos emeralds" was a reference to the game Shadow the Hedgehog, Those are the first words out of Shadow's mouth during both of the endings for the Pure Dark, Semi-Dark, Neutral, Semi-Hero, and Pure Hero stories.

Knuckles seeing something inside the Master Emerald was something that happened during his story in Sonic Adventure.

The gear that Sonic, Tails and Knuckles had were some of the upgrades that they had during Sonic Adventure 1 and 2, like the Flame Ring and Jet Anklet.

Sonic and Shadow remembering Prison Island was a callback to White Jungle and Green Forest from Sonic Adventure 2, and Death Ruins is a forest themed stage from the game Shadow the Hedgehog, hence why Shadow himself was reminded of it in Forest Hill.

Knuckles telling Shadow that Sonic and Tails were right about something was a reference to one of Knuckles' lines during Sonic Adventure.

(4:12-4:41)

One more thing: Apparently, Robo Sonic is called Mecha Sonic on the Sonic Wiki. I didn't know why especially since he's referred to as Robo Sonic in many YouTube videos and games that he's featured in, like LEGO Sonic the Hedgehog. Then one day, I found this YouTube video that showed the evolution of Mecha Sonic battles, and Robo Sonic was on the thumbnail. When I looked at the comment section, the pinned comment said that Robo Sonic is a form of Mecha Sonic, hence why he's called Mecha Sonic on the Wiki.

And that's just about it. Next time, our anthropomorphic heroes and our villains look to find out where and/or when the portal took them.