Equestria's Psychotic Guest (DOOM OC x MLP)

by CrusadingDoomguy

Rating: teen
Tags: Science Fiction, Comedy, Adventure, Crossover, Gore, Violence, My Little Pony: Friendship is Magic, Human, Main 6, Original Character
Length: 4943

Marine, one of the most feared beings in the three dimensions, and he's now in a pastel hell of ponies, Hijinks ensue.

Marine is one of the most feared beings in the three dimensions, Hell, Heaven, and Earth. But, after a portal malfunction occurs as he tries to leave Hell. He succeeds in leaving his domain of fire and brimstone, but, he is not returned to Earth. Instead, he finds himself in Equestria, a land full of magical ponies, and nothing to kill for cubic acres. What happens next? Read on to find out.

Published 2021-05-31 03:40:00 UTC
Last updated 2021-06-14 21:07:49 UTC

Prologue

Hey there, I'm Marine. A few years back, I was blessed by the gods above, giving me great strength and athleticism. Shortly after, I found myself travelling the dimensions and making my name feared. The demons weren't ready for me to walk in with a shotgun and slaughter their race. Being the dipshits they are, they never leave me alone for too long, always have to be on guard.

But that's outside the point. A few weeks back, I was finishing up my rounds in Hell, and began heading back to the mortal realm, what you would call your reality. But then, those little fuckers hijacked my portal and sent me to a random location in the multiverse, planning on sealing me from Hell, never to be seen or heard from again. They may seem like dickheads that run right at you, single-file, waiting to get killed, but they can form a good plan.

Where I ended up, was Equestria, what happened next, is documented here.

Enjoy my suffering.

Chapter 1: Impending DOOM

I woke up in a forest, a dense one, at that. I couldn't see any civilization for miles, just trees, vines and flowers. Grabbing my Combat Shotgun from a nearby vine it was hanging in, I pumped a shell, and took count of the total.

24, Could be better. I set off in a random direction, with the density of the forest disallowing me to know what time it was, or what direction I was heading in.

I soon changed course when I heard screaming. Upon arriving at my destination, I saw no more than 12 wooden wolves surrounding three young, pastel ponies.

Attaching the Sticky Bomb mod for my shotgun, I charged into battle, immediately. Running up behind one and blowing its brains out with a single shotgun blast, I quickly whipped around and fired a Sticky Bomb into the mouth of another.

Predictably, the beast swallowed the explosive, but instead of staggering, like I had expected, it just fucking blew up. Its insides flying everywhere, the creature's blood flying onto my already bloodstained visor.

"Lambs to the slaughter. Who wants some, eh? Who's next?" I challenged, picking them off one by one.

Before I knew it, I was surrounded by wood piles, and some mangled carved wolf bodies. Pumping my shotgun single-handedly, like those guys in Hollywood did it, I looked over to the three youngsters.

"P-Please! D-Don't hurt us! We're too young to die!" The middle one begged. She had a peach colored fur and a red mane, along with a bow. I kneeled down and removed my helmet, revealing the honesty in my eyes.

"Hurt you? I would never, If I wanted to, you wouldn't be sitting here right now." I explained. "Now, where am I, what are you doing here, Where's the nearest civilization, and where can I buy myself a god damn beer?"

"W-Wait, you mean you're not going to kill us?" The orange one asked.

"Why should I?" I responded.

"Well, we trust you, we were here to gather some Zap Apples to help Apple Bloom here's grandmother grow her orchard more." The orange pony cleared things up.

"Ah, that's sweet of you. Little ones, now, take me to the nearest town." I said.

"O-Oh, You mean Ponyville?" The white furred one stated.

"If its got sentient life, I don't care." I said. "Now, let's get going, shall we?"

"W-Well, they might treat you as a monster." The peach one, Apple Bloom, told me.

"Well, I am a monster." I stated.

"W-What?" They all yelled.

I looked back at the bodies behind us. "You see now?" They nodded. "Good, now, what're your names?"

"Ah'm Apple Bloom." The peach one stated.

"Scootaloo." The orange one replied, and I realized she had wings. Strange.

"And I'm Sweetie Bell!" The white one said.

"Huh, nice names, I'll probably get y'all mixed up from time to time." I stated.

"Okay, but, say, Mr. Monster, we never got your name." Scootaloo pointed out.

"Oh! You can call me Marine."

Author's Note

Ahh, my first FimFiction story, I made a similar story to this, with the same main character, but in Wings of Fire, it's my prized story, you can find it on Wattpad, my account name is the same there as here, so go check it out if you want to see my writing style. It's not done, and it'll have sequels, but I might update that more than this. So be patient.

Chapter 2: Meet the Elements

We had arrived in Ponyville after about 15 minutes. Finally orienting myself, I realized it was roughly 12:30 P.M.

"Alright, you three, run along now, and stay outta trouble!" I told the three fillies, as they all went towards a large orchard I saw in the distance. But before I could ease my tension, I heard some dipshit off to my left, roughly 50 feet, scream.

"Monster!! Sound the alarm!!" I looked over at him, and saw an older stallion, older than I was, but not ancient. I'd say about 25-30. He was about to run away, but as he started to turn, I flipped him off.

I kept walking through the streets, ponies looking at me, terrified. I got to the town square, dead center of the whole place. This was where most of the ponies were, and began panicking. But then, they calmed down, and I felt something speeding at me. It would take only about another second for it to hit me, so I stuck my hand out, and felt the force of a turbo-rocket upon my hand.

Glancing over, I saw a cyan pegasus with a rainbow mane and tail, her red eyes staring at me in shock.

"What the-" She began, only for me to send her flying back the way she came.

"That was annoying." I said, brushing my hands off. I began walking towards a big old tree nearby. Reading the sign by the door, I read Golden Oaks Library

Huh, a library, that'll be a good place to learn more about where those demonic bastards sent me. I internally monologued. Knocking on the door, I heard a muffled, female voice yell out to me.

"Be right there in a minute!"

I heard the sounds of cluttering, very quiet whispering, a bit of snoring, and finally, the door unlocking.

"Alright, sorry about the wait, what bring you here- What the haystacks?!"

"Ooohhh, this is gonna be a long visit." I groaned, as this rather bookworm feeling nerd began examining my body.

"This is unlike anything I've seen... SPIIIIIIIIIIIKEEE!" She yelled into the library.

"Uooouuaahhh... What do you want, *Yawn* Twilight?" A young boy's voice echoed back.

"Get me a pen, and some paper! I'm sure Princess Celestia would like to know about this thing!"

"Coming right up..."

A few minutes later, a tiny dragon, just smaller than the unicorn in front of me, clearly drowsy, hand her a slip of paper, and a pen, before looking at me, suddenly waking up, and running back into the library.

"Well, that was awkward." I noted.

"He never does anything towards something new without embarrassing or frightening himself." The mare said. "But that's beside the point, come on in, I need to get some samples." She asked of me.

"Ooookaayyy then...?" I sorta agreed, and she led me inside, shut the door, and began the questioning.

Author's Note

Chapter 2 has been completed at long last and I can finally attempt to publish this!
Now would also probably be a good time to explain the different font colors.

Red is for Marine.
Light Purple is for Twilight.
Same for Rarity.
Applejack.
Pinkie Pie
Rainbow Dash
And Fluttershy.
Default color is for random people that I either, A. Didn't bother assigning a color, or B. Can't find a good color for.

Hope y'all enjoyed this rather short read of a chapter.

Chapter 3: Questionable Ethics

I had been listening to the ramblings of my host for a few minutes now, already getting annoyed.

"What an interesting creature.... It stands on two legs, its muzzle is seemingly nonexistent, and its fore hooves seem to be split five ways at their ends... I've never seen anything like it." She rambled on, writing on a sheet of paper using some sort of magical field, which, I guess was drawn from her horns, as it glowed the same color as the currently levitating objects did.

"Alright, can we move on? I'm bored." I said, causing the unicorn to hurriedly finish her writing, and she handed it to the dragon that had brought us here.

Unexpectedly, he burned it.

"What was that? All that writing to burn it to ash!"

"Calm down, I was just sending a letter."

"Have you never heard of MAILBOXES?!?!"

"Trust me, this is the most efficient way of sending letters to the Princess."

"Okay, I'm confused now, what do you mean?"

She proceeded to explain everything to me. Equestria, the Elements of Harmony, the Princesses, and everything else.

"Interesting... Very interesting indeed." I said So this is where the demons sent me, probably to die alone, and they would have free reign. They'll see. They'll all see, and Pay...

"Hello? Are you still there?" The unicorn snapped me out of my thoughts.

"Yes, just thinking."

"About what?"

"Demons, the past, and a whole lot of death."

"D-Demons? Just where are you from?"

"Hell, where else?"

She was about to answer when a knock was heard on the door.

"Coming!" She then got up, and opened the door, as five more ponies came in, four complete strangers, and one I recognized.

"Twilight! I saw some strange creature wandering around town-" The pegasus from before was going to continue, before she saw me.

"Hello there." I calmly replied.

"Twilight, darling! If you're going to invite guests over, at least try to look presentable."

"Sorry Rarity, he just kinda showed up at my door, and with him being a whole new creature, I got right to studying him! Heck, I don't even know his name-"

"Marine." I said flatly.

"Ah don't think you should trust him, Twi." The orange one with a cowboy hat said.

"I recognize that western accent, are you the relative of a young filly by the name of Apple Bloom?" I asked.

"Ah am indeed, how'd you guess?"

"I rescued her and her friends from a bunch of wolves in the forest outside town. Surprised she hasn't told you yet."

"You took on Timberwolves head on?"

"Hell yeah I did! Twelve of 'em. Complete breeze."

"I don't like him, he scares me." I heard the bright yellow one say, just barely.

"Ah, there's nothing to be worried about, little one. I reassured her. "Now, can I get some introductions here?"

"I'm Twilight, pleasure to meet you."

"I'm Rarity, darling."

"Applejack."

"Rainbow Dash, the fastest flier in Equestria!"

"I'm Fluttershy."

"Don't mind her, she's just a little shy, as the name suggests." Applejack confirmed.

"Hi! I'm Pinkie Pie! We're going to have so much fun!" The final one yelled as she jumped at my face, causing me to fall out of my seat, and my helmet to roll off.

"Aghh, could you try to be a little less loud?" I demanded, grabbing my helmet again, but just throwing it into my inventory.

"As you were saying before we were interrupted?" Twilight reminded me.

"Oh right! I last left off in the firey depths of Hell." I responded casually.

"You mean to tell me you're from Tartarus?"

"Tartarus is the Greek word for Underworld, and Underworld is just another word for Hell, so, yes." I explained. "But if this place does indeed have an entrance to Hell, then I'll be able to get back to kicking ass and chewing bubble gum sooner than expected." I realized, reaching into my pockets for aforementioned gum. "And I'm all outta bubble gum."

"Here you go!" Pinkie said, tossing me a few sticks of mint bubble gum.

"Thanks." I said, putting them away for now.

Another knock.

"Ah, what the hell. What could possibly go wrong?" I said, walking over to the door. Opening it, I saw two Alicorns about my height, roughly 6'3 maybe a few inches taller.

"Oh, hello, what brings you here?" I said.

"Marine! You're talking to royalty! Please try to be presentable!" Twilight urged me.

"Not to worry, faithful student. We received your letter about this creature, and have come to apprehend it."

"WHAT!?!?!"

Author's Note

This took days to write, and is going to kick of the hijinks. Starting in Chapter 4: Apprehension.

Yeah, I know, those of you with a keen eye are probably typing in the comments But author, that would make two chapters in a row have Half-Life names. I don't care.

This took so long to write because I was having PC issues, and kept forgetting to save, and it took me a while to get down the flow of the chapter. My main issues with writing are a shitty imagination, and a shitty keyboard.

Doomguy out!

Chapter 4: Apprehension

Great, I answer a door, and my tendency to jinx myself comes back instantly to bite me in the ass.

"Yeah, capturing me hasn't worked out for anything in the past." I pointed out, remembering the time I got an entire mountain dropped on me by the demons to contain me in a sarcophagus, and I still escaped.

If thou will not go with us willingly, we shall have to take thine by force." The Dark-Theme alicorn responded.

"Good luck." I quipped, loading my double-barreled Super Shotgun.

"Now now, we won't have to resort to violence now, will we?"

Before I could respond, I was engulfed in a golden field, from princess sunbutt over there.

*Sigh* "This isn't fun." A bright flash, and we were suddenly in a castle throne room.

Teleportation, What isn't going to happen to me today? I mentally complained.

"To answer thine's question, thou will not be returned to the Elements."

"Mind reading? Damn you, now I can't even ramble on in my head!" I shouted, thoroughly pissed.

"Now, sister. Let's not get it too riled up."

"If you insist, 'Tia."

"Now, explain to us, creature, just what were you doing with the bearers of the Elements of Harmony?"

"Explaining myself, what else?"

"Then where are you from?"

"Hell. I'm surprised you're not just grabbing information from my mind at this point."

"Thou presents a wonderful idea."

"Ah shit." I cursed myself for that, as Luna began searching through my mind for my memories, when she stopped, she looked traumatized.

"Dear sister, this being is nothing more than a hollow death machine."

"If that is the case, guards! Send this thing to the dungeons!"

"Yes, your majesties." I heard, before being dragged away by a different magic field, still immobilizing me, and I was pulled away to the dungeons, and eventually blacked out.

When I awoke, I was sitting in a dark, torch-lit cave, chained to the wall. Looking around, I realized I had been stripped of the Praetor Suit and was now in more casual clothing. I also realized my weapons had been taken, and I was down to just my fists.

It was about now I tugged on my chains, and broke them, alerting the two guards stationed outside. Both were Pegasi, perfect.

Hitting the floor, I landed right next to my old pair of sickles. Grinning maniacally, I charged at the guards, quickly dispatching them, cleanly stabbing the eye of one guard, and using the other sickle to pin the other guard to the wall.

Pulling the first sickle through the first guard's skull, he dropped dead, and I wasted no time using my momentum to slice the other guard's head clean off.

"Ashes to Ashes, Dusk to Dusk." I muttered, pulling the other sickle from the wall.

Continuing out from the dungeons, I saw other convicts staring at me in awe, some begging me to save them. One look, and I could tell some were innocent, misunderstood souls, which I released. But others, filthy criminals and scum, which I quickly dispatched.

Taking the stairs out of the dungeons, I was now in the lower floors of the castle. Sneakily going about my way, I saw many workers, going about their business, as if a rampaging death machine wasn't on the loose.

I continued sneaking about, until I was about to reach the next set of stairs to head up to the next floor. That's when I was spotted.

"Attention all guards in the lower levels! The creature is on the loose, capture it at once!" I heard announced, before heading up.

Upon reaching the next floor, I saw a sign saying Staircase to floor B2. So I must of been on floor B1. I looked over and saw two guards, analyzing an object I was giddy to see.

The Super Shotgun.

"So, what do you think this thing does?" The first guard asked.

"I don't know, but the thing that had it is probably after it." The second responded, as I appeared behind them.

"Indeed I am, now, are you going to hand it over, or am I going to have to take it off of you?" I said, scraping my sickles together. They turned around, and quickly ran off, dropping the weapon.

"Oh, my baby! How I missed you." I reminisced, ready to kick ass.

Charging back onto the first floor, I realized I was now close to the throne room. Avoiding it, I followed maps on the walls to get to the Alien Artifact Examination Center.

The Praetor Suit must be in there, if I can get it, I should be able to access the rest of my weapons. I thought.

I was semi-correct. As when I walked in, I realized that the group of scientists weren't looking at the Praetor Suit, but rather, the Hazardous Environment Suit, which I had obtained in Black Mesa during a Resonance Cascade an old colleague and I accidentally caused.

Not the Praetor Suit, but if I still have the Vega chip... I internally monologued, reaching into my pockets, and pulling out a small computer chip with the letters U.A.C branded on the front.

Running in, I quickly slid, strafed, and flipped over to it, causing chaos wherever I could. Finally reaching the suit and jumping into it, I heard the familiar voice of the H.E.V Mach IV AI as the suit turned on.

"Welcome to the Hazardous Environment, Mach Four protective suit, designed for use in hazardous jobs." Some nice music started up, but instead of that, I insert the Vega chip into the suit's arm, and suddenly, my robotic ally was back in action.

"Ah, Marine, I see you've found yourself in a rather strange situation. Would you like me to enable access to the Global Inventory Menu?"

"Will do." I replied, and reached into my slipspace to pull out the Chaingun.

"Ah, I see. Playing BFG 10K now."

The metal kicked in, and the Chaingun's barrel spun to life, stepping off of the pedestal where the H.E.V suit was, as I grinned like a lunatic and gave out my battlecry.

"RIP AND TEAR!"

Author's Note

Hoo- Our boy's back in action and craving blood! Since I've been playing HL1 recently, I decided to put some references into here. Along with DUSK. Because why not?

I actually scrapped one idea for the Chaingun scene right there at the end. I was originally going to have a scientist attempt to knock out Marine by throwing a crowbar at him and he'd use it to bash everyone's skulls in. But then I changed it.

Words used: 1,022 (Not counting Notes.)
Paragraphs: 47
Fun writing scale: 10/10

Chapter 5: One Freeman

Stepping down into the fray the scientists guarding my H.E.V suit quickly scattered, Royal Guards flooding in to stop me. I quickly mowed them down, before feeling that damn magic grasp again.

"Not today!" I yelled, managing to regain control of my body, and break the field. Quickly switching to my SMG, I shot a grenade towards a large cluster of guards, giblets flying everywhere. Spraying down a few more guards, I left the unit and began taking a straight shot for the castle doors. If the Praetor Suit was here, I'd get it later, when things were cleared up.

Busting out the front doors, I found myself pursued by several platoons of guards, the exit gate right there. Knowing it would take too much time to push open the doors, I ran straight up the wall, and hit the ground on the opposite side with a roll, maintaining my vertical momentum and converting it to horizontal.

The guards must've been too dumbfounded to follow me by then, so I came sliding to a halt, a whole lot of ponies looking right at me.

"What? Y'all city slickers never seen a jailbreak before?" Just then, they all started screaming and running, and in the fray, Twilight and her friends finally showed up. "Huh, little late there for a breakout, y'know."

"Well ah'm afraid we got caught in a big 'ol kerfuffle just tryn' to find ya." AJ replied.

"There was the issue of getting here, persuading the Princesses to let us see you, then trying to find you, then follow you. Then now." Twilight explained.

"So what're we waiting for? Let's get outta here!" I suggested. As sticking around didn't seem too good. Just then, old hags Light and Dark showed up to stop us again! "What is it this time?" I groaned, having had enough of these bastards.

"As it stands, creature, you are too strong for our guards to contain, and it has been ruled by the council that you be sent to Tartarus at once."

Fools, that was exactly where I needed to be. "Oh no what ever will I do?" I said with extreme sarcasm. Before getting a scowl from Moonbutt, and teleported to Tartarus, along with the Mane 6, Brightass, and Dark over there.

My exitement was quickly diminished when I realized it actually was not Hell. More a cave locked away somewhere like a maximum security prison.

"Oh come on! This is boring! Where's the fire, brimstone, nations of demons running amok doing everything they can to kill me? What kind of cheap knock-off is this?" I demanded.

"We do not know of the place you speak of."

"Really? Y'all went diggin' around in my mind, and you DIDN'T see any of that? That's Hell, where the souls of the damned are turned into Argent Energy. An infinite fuel source that allows the demons to reach new worlds to conquer. The reason I bring this up is because Hell is another word for Tartarus."

"But explain, how does this have to do with you?"

"The demons sent me here to get rid of me, I was the one thing stopping them from getting out of control and taking over the multiverse. After an old friend of mine was locked up in a stone sarcophagus again, until he is needed.

"So what you're saying is that those creatures are evil?"

"Yes, what connection between 'Hell' and 'Pure Evil' can you not see?"

I heard Celestia mumble some things, and whisper to Luna, yes, I know their names, I just didn't want to use them. But anyway, once that was over, I was told that I had been relieved of all crimes. Which was nice.

We were then teleported back to the Golden Oak Library, where this whole shebang had started, and finally, Celestia and Luna bid their farewells, and we could get back to our own thing.

"Well, that was annoying. Where were we?" I asked.

"Where we were is unimportant, Marine." Twilight said.

"She's right, the princesses were acting awful strange when you cleared things up."

"I kind of hate to admit it, but she is right."

"Whaddya mean?"

"Well, they never usually loose their composure around us, but you saw the way they got a bit anxious when you mentioned the demons?"

"Not only that, but they were also whispering to each other, something they never do!" RD pointed out, and now I felt stupid because I didn't know that was something out of the ordinary.

"Indeed, there must be some deeper conspiracy surrounding you three."

"Like what?"

"Marine, can you not see! Don't you think that Celestia and Luna might of been in league with the demons?"

"That would seem logicaaallll-" I began as the realization hit me harder than a knockout punch from a Baron of Hell.

"Oh shit."

Author's Note

Okay, I'll stop with the HL related chapter names. For now.

My summer vacation started, so I'll have loads of free time to write. Yee-

Also, since it's been fucking years since I last watched MLP. (Season 2's release, I know.) So I made up and definitely screwed up some aspects of MLP as a whole. So don't judge.

But also, BOOM! Plot twist! This'll add some more spice to the pan, and also kinda delay going through some show events, but I'm not planning anything too crazy just yet.

Keyword yet.

Chapter 6: Conspiring and Planning

The idea of the Princesses working with the demons made sense.

The demons sent me here so I would let my guard down. Whilst influencing them from within. Then they would strike full force, and I wouldn't be ready, and I would be swiftly overpowered. Equestria would be taken, and they'd have alicorn magic.

Immediately, we began planning our next move.

"I say, we grab the Elements, rack up every single troop we have, and we run in and kick their butts!"

"That won't work, for one, I do believe the demons are immune to the Elements.

"Besides, it has been proven that the Element's effects aren't permanent."

"Twi's right, when Nightmare Moon appeared and we first met up, she had been sealed away on the moon by the Elements."

"Although they may not be permanent, I think the Elements would still be invaluable to our mission."

"You're right, darling, while we may need a more complicated plan, the Elements could help with it."

"Y'know what else would help?" I asked.

"The Praetor Suit." Vega responded.

"Yeah, while the Hazard Suit is nice and all, it wouldn't help much against the demons, maybe against the American Military, but the Praetor Suit would be much better suited."

"Indeed, I suggest our first order of business is reclaim the Praetor Suit. But to do that, we would have to get it from Canterlot."

"Yes, but, that would take a long time, and who knows when they might show up?" Fluttershy pointed out, I forgot she was there.

"Yes, but who said anything about conventional travel?" I quipped.

"I see what you are hinting at, and while it might take a long while, it would certainly be faster."

"Marine, you're not suggesting we-" the voice of other robotic companion, Dr. Samuel Hayden began.

"I have began research on designing a weapon capable of allowing a projectile to fly at incredible speeds to travel between any city we've been to accurately and much more efficiently."

"You're insane, you know that?" Hayden told me.

"Yep."

Upon grabbing some Anomalous Materials we had the Ion Catapult, Medival version created within three, maybe four hours.

"That is a weapon, not a teleporter." Hayden told me.

"Did that stop us last time?"

"Sadly not, it also didn't stop you and the Slayer from blowing a hole into the surface of Mars..."

"Speaking of the Slayer. Vega, get all the information you can on where we are and attempt to open a portal to the Ingmore Sanctum ASAP. You never know when we might need a seasoned professional on the scene."

"Gathering data now, this may take several weeks."

Back to the mission at hand, we quickly loaded it up. With myself as the projectile, and fired, sending me flying through the sky, eventually landing smoothly at the entrance to Celestia and Luna's castle.

Walking right in like I owned the god damn place. Right to the Alien Artifacts Research Unit. I teleported the Hazard Suit to the Armor section of my inventory.

Walking deeper into the unit, I saw the Praetor Suit, standing idle above the scientists. Walking in, the petrified scientists stepped aside as I waked up to the green beauty of the Praetor Suit.

Putting my hands up to it, demonic images flashed in my mind, and soon enough, I was back inside the familiarity of the suit.

Pulling up the helmet and dusting off the visor, and admiring its gray, stylish beauty, I quickly placed it on my head, checked the weapons section at long last, everything checked off. I then managed to get a vantage point to jump, dash, Meathook, and Gauss Jump my way back to Ponyville in minutes.

"Mission Accomplished." I said. Dusting myself off.

"Alright, now that we've got ourselves a fightin' chance, what's next?" Applejack asked.

"We plan our attack." I said, and we got down to business.

Author's Note

I couldn't find a decent color to use for Dr. Hayden, so I'm making Luna's text dark purple instead of the blue that it was. But yeaahh, Finally got off my lazy ass to write this.

But yeah, shit's going down now!

Also, the Praetor Suit uses the Classic Green design, for completing the Super Gore Nest Master Level in the Classic Mode on any difficulty. Just an FYI