Hi everypony! And hi there, Sonic fans! This here is my first crossover from this two marvelous series that are part of my fanbase. I must advice you that this fic is based in part of Gears of War, and you'll notice it in various elements like Sonic's attittude or the weapony used. So if you don't like grimdark fics, don't read this. This fic contains strong language, blood and gore (at least the first chapters no), some sexual content (in future chapters, like in Act 4 or something like that).
This story is settle in Alternative Dimensions, so this Mobius is completely devasted, while everyone is a little older (the Mane 6 are 18 years old except for Fluttershy, the Cutie Mark Crusaders, Cosmo and Tails are 14 years old, and SOnic is 21 years old)

Notes: The "Gates of Infinity" mentioned here are from another fanfic I'm making, "Sonic Infinity". Unfortunately just the prologue is in English.

This story is based upon the SatAM continuity, that's why Snively is the Villain and The Knothole Freedom Fighters exist.

Prologue

The Multi-verses of Earth, a constant growing mystery for the inhabitants of this planet and its multiple faces. Millions of Universes exist without even noticing the existence of the other, yet all connected by a powerful Sub-Spatial bond known as the Infinity.

These worlds are pretty similar between them, but at the same time very different. Worlds like Mobius, where humans coexist alongside intelligent humanoid animals called Mobians; and Worlds like Equestria, where no human exist, and the ponykind takes the role of mankind in a world surrounded by mythology.

It's curious that the encounter of these two worlds could have such consequences that almost destroy the balance in the Infinity…

Its year 3238 in Mobius, and the planet is completely in ruins. The evil Dr. Ivo Robotnik conquered the world many years ago with the help of his army of SWATbots, destroying anyone who opposed him, except for the Knothole Freedom Fighters, an army of rebel Mobians who desired to restore peace in Mobius. The war between the Robotnik Empire and the Freedom Fighters was fierce, and it took many innocent lives, yet it seemed to end with the death of Robotnik at hands of the leader of the Freedom Fighters Delta Squad, Sonic the Hedgehog.

But the war didn't finish there. Soon after his death, the evil genius Snively, Robotnik's nephew, took the leadership of the Robotnik Empire, and launched massive attacks to the Freedom Fighters and any other ally they had, although few he could do to stop Sonic and his squad, remarkable heroes that seemed to push the evil scientist into the edge. Victory was close for the Freedom Fighters, yet destiny was not on their side this time.

Snively secretly found out that the Universe of Mobius was about to collide with a new different Universe, and that clash could enable the Robotnik Empire to transport their troops to that World and conquer it. Without the Freedom Fighters noticing, he built a portal that could enable such desire. At last the day of the collision happened, and thought no one in Mobius noticed it or even cared, the strange disappearing of Snively was suspicious. But even with its leader away, the army of SWATbots kept attacking the main Mobian cities.

Luckily for them, Sonic found the portal Snively built, and knew that it could be dangerous to keep him in a new world, with the danger that he was getting stronger alongside with his empire, and was determinate to chase him back to Mobius, but it was late. The rest of the SWATbots destroyed it, and with it any chance of reaching him. Or at least they thought so. The rest of the Freedom Fighters were able to locate a still functional portal in a wretched building outside of New Robotropolis. It was risky, but anyway Sonic and his friend, Miles "Tails" Prower the Fox, decided to investigate the zone, expecting to find the portal that could lead them to this new world.

Meanwhile, in Equestria, strange things were happening. Although the terrible Nightmare Moon was defeated many months ago, a new evil force was invading the once peaceful world. As if they were dark demons, strange robots came from the Everfree Forest, and began attacking small pony cities. They were just small ultimatums, and nopony felt really in a dangerous situation. Unfortunately, this leaded to the capture of Hoofington. The city was surprised by the attack of the curious robots that began destroying everything and capturing everypony, all of them under the lead of a really weird creature previously unseen in Equestria. This creature called himself "Snively", and demanded the surrendering of Equestria in order to prevent what he called a "really unnecessary ponycide".

The message reached the ears of Princess Celestia, one of the rulers of the land and Deity of Sun. The last she wanted was starting another war, cause the last one 1000 years ago left the land in complete misery; but he couldn't let her people be slaved by an unknown being that self-acclaimed himself as the new ruler of Equestria. She was in despair, but knew that there was someone who could help her to stop the evil tyrant, her faithful student Twilight Sparkle, who alongside her friends, now named the Mane 6, were able to stop Nightmare Moon. But while she was busy trying to advise her student, Snively was planning his next attack. With the Freedom Fighters still in Mobius, he built his most powerful weapon, the SWATbots Battle Cruiser, a powerful space battle cruiser equipped with Orbital Cannons. He was ready to launch all the three completed models to destroy more Equestrian cities, including Ponyville, the home of the Mane 6.

Both Universes were now fighting a common enemy, and the fate of their worlds was in the hands and hooves of the Delta Squad and the Mane 6…

Act 1: Assemble
Chapter 1: New Lands

Opening their way through the ruined building, members of Delta Squad, Sonic the Hedgehog and Miles "Tails" Prower, were in a hurry to find the portal supposed to be located there. They were armed with their Shotguns and Assault Rifles. Using the very useful Chainsaw Bayonet attached to their rifles, the two Mobians finally reached a small chamber equipped with a giant computer and a strange arc-like "door". It was the portal they were looking for.

- I never thought we could really find it. – Tails said really happy to found the portal.

- Never? Please, give me a break. You were the one who was really sure here it was. – Sonic answered in a little cold way.

The hedgehog used the communicator attached to his right ear to contact the rest of the Freedom Fighters in Knothole.

- Control, do you read me? We have found the portal, but it seems to be offline.

- Sonic, is that you? – answered a woman voice. – It's me, Sally. Aren't you happy to hear…

- Sally, I've told you this is serious business. – Sonic was a little annoyed with the lack of seriousness from her around the whole portal thing – Just because we hang out means we've got to lose focus on the mission.

- I'm sorry, Sonic. It's just…well; you are only focused on the war that you don't pay me much attention.

- I'm also sorry, but I think is more important to end this war rather than spending a little more time with you. Especially now that we're so close. – the hedgehog tried to sound the lest sharp as possible.

- Ok then. – she said a little sad – You said it was offline? Maybe you can use NICOLE to find a way to reactivate it.

- Got it. We'll keep you informed around this.

After finishing the contact, Sonic sighed. He was a little sad, and Tails knew why.

- Sonic, when are you gonna tell her?

- I don't know, buddy. She's so in love with me, and I don't wanna break her hearth.

The hedgehog was Sally's boyfriend for around six months, but nowadays he didn't feel the same for her, and he wasn't sure if what he felt for her childhood friend, Amy Rose, was really love…or just interest in making her happy.

- I envy you, Tails. You don't have to live this with Cosmo. You're so in love with her.

- Believe me, friend. I was even worse than you before meeting her. If you don't believe me, just ask Mina. – Tails said trying to raise his friend's mood, remembering him how he spent a time with Mina Mongoose.

- Yes, I remember. But I also remember that we're here for something. NICOLE, – Sonic directed to what seemed to be just empty space – We need you to find a way to reactivate the energy here.

Out of nowhere, a curious hovering robot appeared, targeting into a small terminal in the nearby computer.

- You and Rotor did a great job with her new body, Tails. – Sonic referred to the new appearance of NICOLE, who was previously more like a computer.

- I know, buddy. Too bad we didn't have time to add a voice feature for her.

- And why do you think I congratulate you? She was so annoying talking. – Sonic said sarcastically, referring to NICOLE's talking to him.

At last the robot was able to restore the energy in the chamber, activating the computer and the portal, whose arc was filled with a mysterious liquid screen. In the computer, a holographic image that represented Mobius was displayed alongside what seemed to be another planet exactly like Mobius, but there was still something different in it.

- Tails, what do you think that means? – Sonic pointed to the screen.

- Well, I believe is the world Snively crossed to. Apparently Mobius collided with, or backwards.

- In few words?

- It's the connection between Mobius and that new World.

- Alright then. NICOLE, try to connect the portal with one of that world. And please, check out it is safe.

The robot began hacking the computer to align the two portals, while Sonic and Tials argued about the portal located right there.

- Hey Sonic, why could someone have a portal like this in Mobius?

- Ask that to the fucking owners of this place.

- For what I remember, it belonged to an organization known as "Gates of Infinity", but they disappeared years ago. This building must have at least twenty years.

- But at least they left this portal for us, and that's all that matters.

After few seconds, the screen now showed two red flashing points in both worlds. They deduced they represented the portals.

- Sonic, I've received data from NICOLE. It seems that the portals are now aligned. Unfortunately, we don't know if the communicator will work through the new world.

- Received, Control. We'll recover transition as soon as possible. – He finished the transmition and finally told Tails – Let's get through this shit.

Sonic approached the portal, and slowly began crossing it. At first it felt like entering water, yet everything changed after a while. Suddenly, the blue hedgehog was in a completely different environment. It looked like an armory. Tails followed Sonic shortly, and noticed that most of the armory seemed to be designed for equines.

- Holy shit! Now where are we?

- I'm clearly not the right hedgehog to answer you. – Sonic was still calmed, but yet surprised with this new world.

Meanwhile, in Ponyville, everything was still peaceful, although the recent events in Hoofington were alarming everypony. But the arrival of Snively was something everyone was talking about, but also something that bothered Twilight Sparkle, a young unicorn pony, of around 18 years, owner of the Magic Element of Harmony.

She was expending most of her time at her home, the library, reading about the curious being that recently arrived Equestria, yet she found neither about him nor about the strange robot army under his control. Yet she found some interesting data that could explain what happened.

While she was reading, someone entered through the door of the library. It was Spike the Dragon, who went for some shopping and trying to flirt with Rarity, Twilight's friend and Spike's crush. As soon as he saw Twilight he began asking many things around her reading.

- Hey Twilight, what's going on? Why have you been reading so much these days?

- I'm sorry Spike, but it's because something's bothering me around the Hoofington incident.

- Oh please! Don't tell you believe those rumors.

- Those are no rumors! Yet I couldn't find anything about robots in Equestria like those described by "rumors", neither about Snively or whatever his species are called.

- So? If they don't exist here, it's obvious that it's a lie.

- Well, how do you explain this? – Twilight showed the purple dragon an illustration that represented many similar looking "planets" connected by a curious cosmic network.

- Eh…In first place, what is that supposed to mean?

- It's a nexus, Spike. A nexus between Alternative Universes, different between them. For example, Equestria's one Universe. This network, called in the book "Infinity", links this world with other different, yet traveling through it could be dangerous.

- You see? DANGEROUS! There's no way…

- But here it says that sometimes Universes may collide, which enables a fast, immediate transport between Universes.

- Wow, wow, wow, hold on your horses, Twilight. Are you telling me this…Snively comes from another world…which has collided with Equestria.

- Yes, that's what I mean.

After hearing this, Spike bursted in laugh, much for Twilight's anger. But right in that moment, he belched up a small scroll. It was sent by Princess Celestia. As soon as she saw it, she took it and began reading it.

- Twilight, what does it says?

- Shhh! I'm reading it.

The scroll said:

"To my Faithful Student:
By the date you must be aware of the recent incident in Hoofington. All our efforts to negotiate with Snively have failed, and the only answer we got was a menace of attack. There are some things which I must talk with you, so please come to Canterlot as soon as you can.
I know is still too soon to tell this…but Equestria might be once again in war, and I'm not pretty sure of how everyone will handle this.
Sincerely,
Princess Celestia."

- No way… - Twilight Sparkle was speechless. Equestria in war? That was impossible.

- Twilight…why you look so worried? – asked Spike after seeing her "big sister" in shock for what she just read.

- Spike, reunite the rest of the girls and prepare the balloon. We're going to Canterlot.

- To Canterlot? Alright then. – Spike left in a hurry to reunite the rest of the Mane 6, but before leaving, he asked one last thing – But what are you gonna do?

- I need to get some things ready, Spike. Now hurry up, we got no time to lose.