Introductory A/N:
Hey guys, before the story begins, I thought I'd give you a bit of insight on the story's background, so you don't have to ask in the future.
This story is quite complicated, it is the result of many years of consideration as to how to write a really good crossover story between Mario and Sonic, which satisfies all types of fans. See, I have had too much inspiration for this story to list. As it happens, my main focus was to set this story apart from the animations I was inspired by, by focusing the setting around Sonic's home-world, as opposed to Mario's. The latter of which tends to be more frequent in the GOOD animations I watch. I am a huge fan of Mario and Sonic, and I have been in love with their respective franchises since the day I discovered a game called 'Ultimate Flash Sonic,' the first online game I ever played, on the internet - when I was merely four years old. I am extremely passionate about writing, and I could go on forever about the background of this story. I just hope that I meet my younger self's expectations for a really good Mario & Sonic crossover, that is my ultimate goal here. And of course, I hope you enjoy it too!

~ THE NEW ARRIVAL ~

Mario stood by Princess Peach on the balcony of her castle as fireworks erupted in every direction. Cheers and whistles of pure joy echoed from beneath them as the entirety of the Mushroom Kingdom celebrated their victory. After years of constant battling for World Peace, the feud between the Mushroom Kingdom and Bowser's Kingdom had finally come to an end. Bowser had given up his antics and agreed never to attack the kingdom again, and never to cause any harm to Mario, Peach, or anyone else, either. Bowser had settled down with his new bride-to-be, and the peace finally came to the kingdoms. Peach and Mario had found love in one another too, as well as Luigi and Daisy, just as everyone had predicted. The tetrad were quite the couple, now that the battling for freedom was over.

However, not everything is as simple as that... while Bowser had retired from his mission, his offspring, Bowser Junior was quite infuriated by his father's impotence, and seized control of Bowser's former army, launching one last attack on the Mushroom Kingdom.

Bullet Bills everywhere, crashing down upon the homes of millions of innocent citizens, fireballs burning down the nature reserves around the border - Bowser Junior's airship was headed straight for Peach's Castle, with Bowser Junior himself standing on the head of the ship, glaring down upon his arch-nemesis.

"MARIO!" Junior roared, clenching his claws as Mario slammed a Banzai Bill away from a crowd of Toads. Luigi dove towards a cannonball, knocking it back towards the airship with his infamous hammer. The plumber brothers jumped back to the balcony, where they protected Peach from the incoming airship. Junior hopped down onto a bridge at the bottom of the airship, and stood at the very edge, hands on his hips.

"The time has come, Mario! Tonight shall be your fall! I will now complete the mission my father failed to execute, time and time again!" Junior bellowed. The Toads beneath him ceased their screaming, and listened in terror as a fleet of armed Koopas rounded them up and forced them into a confined area. Mario snarled as he leapt towards Junior, reaching out and winding up his fist for a powerful hit. Bowser Junior was ready for this, however, and smacked Mario away with a strange wand-like contraption. Mario's cap was knocked into the distance, and Mario fell to the ground. Luigi screeched and rushed down to the ground to catch him. Luckily, Luigi broke Mario's fall, but his hat was nowhere to be seen. Peach screamed as Junior summoned a large thunder cloud over Mario and Luigi's head. Junior roared with maniacal laughter as he twirled the wand in his hand.

"This is it, Mario! With you gone, I will rule over the Mushroom Kingdom, WITH OR WITHOUT THE PRINCESS!" Junior cackled, as the lightning danced within the cloud.
"Mario, NO!" Peach cried out as Mario and Luigi stood up.

"Smell ya later, MARIO BROTHERS!" screamed Bowser Junior. Red and black lightning erupted from the cloud with a vicious thunderbolt, and it struck Mario and Luigi with the force of a thousand hammers. The two brothers shrieked in horror as they vanished from the area, leaving only smoke behind them. The cloud vanished, and Bowser Junior stood victorious over the Mushroom Kingdom. It truly was game over..

Sonic and Shadow flung themselves into Tails' base, panting and full of adrenaline. Tails turned to stare at the two in confusion, and they pointed to Tails' training room.

"Sorry we're late, buddy, but SHADOW here got into a little predicament with Knuckles!" Sonic rolled his eyes.
"ME?! YOU are the one who had the nerve to mock me and call me inferior to that so-called guardian!" Shadow snarled. Tails chuckled as he watched the two quarrel.
"I'm sorry guys, but Sally went home. She was tired of waiting for you guys when you're late to her Yoga class every week," sighed Tails.
"I only go to spend time with her!" Sonic pouted, "And Shadow goes because Amy's relaxation techniques are... disturbing."

Tails nodded, laughing, and hopped down from his stool, holding a box of equipment, "You caught me at a good time though. I wanted to show you something I just made!

Shadow frowned, "Another pointless device?"
"Awe, come on Shadow, appreciate his hard work!" Sonic scolded, "Uh.. what is it, Tails?"
"It's a Multidimensional Amplification Generating Navigational Experimentation Tripod," beamed Tails.
"Multidimensional.. amplif-... generating.. what?" Sonic tilted his head.
Tails shook his head and chuckled, "It's called the M.A.G.N.E.T, it's a three-piece device used to detect interdimensional artifacts or life-forms!"
Sonic pretended he understood what Tails meant, and began nodding slowly. Tails hooked the device to his wrist and it curled over his hand. The three pieces latched onto his first, third and last finger, respectively. Tails showed it to Sonic, but Shadow didn't seem to be taking much interest. Technology never was his thing.
"Interesting..!" Sonic smiled awkwardly.
"Sonic, I know you, you have no idea what I'm talking about and you are questioning the point of this thing's existence, right?" Tails smirked. Sonic nodded faster, feeling a bit guilty - "Well, for starters, earlier today I picked up a strange energy coming from the edge of our galaxy, and now as it turns out.. I can see what it is! It seems to be some sort of one-dimensional life force, squeezed into a kind-of invisible container and surrounded by energy, I've never seen anything like it..!"

Sonic's ears perked up, he snatched the device from Tails and latched it onto his own hand, staring at the contraption. It began to light up as it reacted to a frequency coming from outside. Tails gasped and dragged the two hedgehogs outside, only to witness two silhouettes crashing down into the beach nearby. The trio stared in shock for a moment, and then rushed to the beach to investigate. They stared down at the two humans, surprised and confused.

"You don't think they're.. y'know, Eggman's, do ya?" Sonic looked at Tails.
Shadow shook his head, "No, they look harmless."

One of the figures wore a cap, while the other was hatless. They wore matching outfits, but one had a red shirt, the other had green.

"They look familiar for some reason, but I can't put my finger on it-" began Sonic, but before he could finish, the human in the green shirt let out a petrified scream.
"Oh, he's alive," Shadow chuckled, as the green shirt guy scrambled away from them. He was shaking, and seemingly intimidated - "See? Told you they looked harmless."

At that moment, the man in the red shirt rose up and stood parallel to the two hedgehogs and the fox. The man appeared confused, and clueless as to where he was - moments later he broke into a fit of rage and turned, screaming gibberish at the sky. Sonic and Tails looked at each other and shrugged.

"Uh, you okay dude?" asked Sonic. The man turned around and let out a deep sigh. He began explaining what was going on, and called over the other man. Tails frowned and lead the group back inside his laboratory to sit down. He gave the two men some food, and the man in red continued his story.

After a few minutes, Sonic recited the man's explanation to make sure he understood what was going on.
"So your name is Mario, this guy here is your brother Luigi, you come from another dimension, where you finally defeated your arch-enemy, but his son attacked you and somehow he made you wind up here?" Sonic tapped his fingers on the table they sat around.

Mario nodded quickly, Shadow huffed.

"Why does your brother have a hat and you don't? Aren't your outfits like, meant to match or something?" Sonic questioned. Mario's eyes widened - he looked up at his hair and gasped, there was no hat. He groaned and slammed his head onto the table in misery.
"Ohhh.. did Bowser Junior make you lose your hat too?" Tails asked sympathetically. Mario nodded sadly. Luigi shoved the rest of his food into his mouth, hoping that the others would not notice.

"Well, we'll help you get back home! Right guys?" Sonic stood up, happily.
Tails jumped up in a supportive manner, "Right!" Shadow simply shrugged. While Mario thanked the trio, Luigi began exploring the laboratory, fiddling with random equipment and trying to figure out how some stuff worked.

Sonic turned to Tails, "Hey buddy, is it okay if I keep this MAGNET thingy-ma-bob with me for a while?"
Tails paused for a moment and thought, "Well, uh.. it's still in prototype, but sure, I guess, why not?

Sonic nodded and gestured for the group to follow him. They made their way towards Park Avenue.

The Quintet made their way to a flat rented out by some of Sonic's buddies, and made their way into Sonic's room. Luigi wandered off to tamper, Shadow leant against a wall in a dark corner, and Tails sat down to fix his 'Miles Electric.' This left Mario and Sonic alone in the center of the room. Mario admired the room around him as if he'd never seen Mobian Tarpaulin. Sonic grinned and revealed that he had been holding onto a strange green gem. Mario turned to examine the gem, but remained clueless.

"You don't know what this is, do you?" Sonic asked. Mario shook his head, not taking his eyes off of the mysterious artifact.
"This is a Chaos Emerald," Sonic continued, "one of seven gemstones withholding the power of true ultimatum. Nobody knows of their origins, only that if one can withstand the power within all seven at once, they can unlock the power of chaos - hence the name. Shadow and I are currently scavenging South Island for emeralds, as usual, because our arch-enemy Doctor 'Eggman' Robotnik has attempted to seize control over Mobius once again. Unlike last time, he's taken a more subtle approach, which only our spy forces have been able to gather details about. He's sort-of.. redeveloped this robot, which is his speciality - a doppelganger of myself, known as Metal Sonic. Metal Sonic is infamous as being my artificial arch-enemy, but it seems as if he's had his greatest upgrade yet now. Eggman's collected scraps of failed projects over the years and rebuilt them altogether to create his ultimate weapon.."

Mario, at this point, was staring at Sonic - his eyes were filled with interest and suspense as Sonic paused.

"He calls it the Mark VI, whatever that means. It kind-of resembles me, but also it's completely different... I dunno, I can't really explain it."
Mario frowned as ideas of its appearance flooded his mind. Was it Sonic but made out of metal, or was it something completely different? Whatever it was, it sounded dangerous.
"Anyway, that's why I- we need to find the seven Chaos Emeralds, so we can stop Eggman and the Mark VI before they get any further with taking over the world!" Sonic concluded. By now, Tails was standing next to him, smiling, and Luigi had stopped messing around so that he could listen in on the conversation as well. Shadow, of course, remained in a secluded corner. Mario and Luigi glanced at one another, flames of determination blowing in their eyes. They jumped into the air with a cheer and landed in a very intriguing pose, appearing to be gesturing something to Sonic and Tails.

"Huh, so you think that after we take down Eggman and the Mark VI, you can use the Chaos Emeralds to go back home and save the Mushroom Kingdom from Bowser Junior? And you'll help us beat our enemies?" Sonic's eyes lit up in sparkles. Mario and Luigi smirked and nodded enthusiastically.
"Alright, this is awesome! We're a team now!" Sonic beamed, turning to Shadow, "Right Shad?"

Shadow merely huffed.

"Alright, I've rebooted the Miles Electric and fixed all the broken parts, we should be able to use it to locate the closest Emerald from here!" Tails revealed his innovative device. Finally, Shadow joined the group, and all five of them eyed the radar device. It seemed that there was an emerald not too far from here, located in a place called 'Emerald Hill.' Sonic and Tails smiled at one another, and then turned to the door.

"Hehe, this'll be a piece of cake. Tails and I know Emerald Hill like the backs of our hands!" Sonic laughed, leading the quintet out.
"But we all wear gloves.." Shadow mumbled, slamming the door behind him.

Meanwhile, a miniaturized drone hovered just outside of Sonic's window, it seemed to be carrying a small camera, which was recording footage of everything that had just happened.

"So.. Sonic, Tails and Shadow have a new buddy.. the Super Mario Brothers, eh? Well, I suppose a few extra bones to feed to Mark VI won't be too much.." a malicious voice echoed from the other side of the camera, followed by maniacal laughter.. ongoing, and terrifying.

Two and a half hours later, the quintet arrived at the border to Emerald Hill.

Without hesitation, Sonic turned to his friends behind him and chuckled, "Let's make this interesting. Try to keep up!" He then turned to dash off into the distance, but before he could, a pair of metallic boots smacked against his torso, sending him hurtling back into a large boulder. The rest of the group armed themselves with their respective weapons, and growled at the silhouette that attacked Sonic. Mario and Luigi had no idea who they were up against, Tails simply tilted his head. Shadow, however, appeared extremely on-edge. From the shadow cast over them by the silhouette, came what appeared to be another Shadow, but with yellow quill stripes instead of red.

"An android," Shadow clenched his fists. Mario and Luigi gasped, drawing their hammers from their pockets. The android chortled at the group, rushing forward to slam his boots into Shadow again.

Shadow, on the other hand, was ready for this - and teleported out of the way with just enough time to grab the android and whirl him into a hill. He then followed this up by teleporting to the android and pinning him against the wall, snarling.
"Who sent you here? Why are you following us?!" He bellowed. The android resisted, but it was simply futile.
"I'll.. never.. ugh- t-tell yo-u-u!" The android sputtered, sparks flying from his body. Shadow's grip around his neck only tightened.
"I'll crush every artificial bone in your body and use your oil as a slide to give my skates an extra boost, if you don't spit it out now," Shadow warned. The android gulped, and with a sigh, he accepted that he had no other choice.
"My master, Doctor Eggman sent me, he wanted me to slow you down.." explained the Android.
"Slow us down? Why? We haven't even retrieved a single emerald, yet.." Shadow questioned.
"So he could have time to do this," the Android smiled, pointing up at the sky.

Within moments, it had gone from a clear, beautiful blue to an eerie shade of grey and red. Lightning rippled through the clouds and with a horrific clap of thunder, struck Emerald Hill. The zone lit up in flames, forcing the critters in the area to flee for their lives. Screams filled the air in every direction, as the team gasped. Luigi caught sight of Eggman hovering away with a Chaos Emerald in his Eggmobile, and gestured for the others to follow. Tails pulled Sonic out of the boulder, and everyone chased Eggman, still shocked that Emerald Hill was burning.. just like that.

"FOOLS! YOU'LL NEVER CATCH ME! WITH THE POWER OF CHAOS IN MY GRASP, I CURSE YOU!" Eggman roared into his megaphone. He lifted the emerald with a dramatic movement, and swiftly swept the ground with a bolt of lightning, blocking the quintet's path.

"No path is too tough for us!" Sonic grinned, holding out his hands, "EVERYONE GRAB ON!"
The team all latched onto one another, and Sonic released a powerful discharge of energy.

"HERE WE GO!" Sonic yelled. Surrounded by a blinding blue light, they blasted through the blockade ahead and caught right up to Eggman.

"Not so fast, pests!" Eggman revealed three laser cannons, and opened fire. Mario and Luigi pulled away from the group and used their hammers to deflect them. Shadow used his chaos energy to destroy the lasers before they made contact, and Tails used his ability of flight to lift Sonic above the lasers.

A giant bomb landed on the ground ahead, Shadow took the lead and leapt over the bomb, using a Chaos Spear to rebound it into a wall. Rubble flew in every direction - Mario and Luigi leapt onto the pieces, bouncing off of them and spinning together in mid-air to launch a powerful double attack. Eggman turned, gasping as the duo smashed into the Eggmobile, sending Eggman flying into the distance. A yellow Chaos Emerald hurtled down to the ground. Sonic made a break for it, boosting himself forward once again, but for once, he was too slow - another silhouette flew across the sky and snatched the Emerald in mid-air, landing on the ground in front of Sonic.

"What the hell?!" yelled Sonic, as he glared at the silhouette.
"I'll be taking this..~" murmured the figure, barely audible to Sonic.
"Hey, give that back! Finders keepers, man!" Sonic kicked dust from the ground as he tapped his foot impatiently.
"Find it then...~" the figure chuckled, vanishing from thin air. At last, the rest of the team caught up to Sonic.

"Damn... almost had it..." Sonic grumbled under his breath.
"What the hell was that?!" Shadow bellowed. Mario and Luigi looked at one another, Tails tried to see if his Miles Electric picked up any familiar heat signals from the creature - yet to no avail.
"I have no idea.. but whatever it was, it's fast.. really fast, and quiet, too. When it spoke, it was almost like a mumble.. so weird," Sonic stared ahead.

Mario, Luigi, Sonic and Tails turned to pay a moment's respect to Emerald Hill, which was rapidly burning to the ground.. it was too late to stop it. Their moment of silence was quickly broken by Shadow's lack of patience and tolerance for time-wasting.

"Damn it, Sonic! You and Tails can mourn the symbol of your friendship later, we have a job to get to!" He shouted, and the team snapped out of their quiet phases, returning to their normal selves as they walked off into the distance; Shadow lead the way.

While the others talked, Sonic couldn't help but stare at the ground, analysing what had just happened. It was all going on so fast.. how did Eggman get a hold of that Emerald and know how to destroy an entire zone with its power? Who was that creature that snatched the Emerald, and how did it use Chaos Control with no lag time?

"And why..?" Sonic thought out loud. Mario stopped walking and turned to look back at him, he asked if Sonic was okay.
"Yeah dude, I'm fine. Let's keep moving.." Sonic reassured Mario awkwardly. Mario sighed sympathetically, and with a nod, continued walking with the rest of the team.

Next stop: Station Square.

TO BE CONTINUED.