A/N: I was looking through various fictions one day when I found out that there were no Crossovers between Left for Dead and Mass Effect, when I thought about some of the Alternative Histories of Earth in Mass Effect it suddenly hit me, wouldn't it be awesome if a Charger was to fight next to Wrex, a Jockey chatting with Mordin, a Witch kissing Samara, (forget the last one) the possibilities were bloody endless, and so many different OC's at that, throw in the evolutionary talent of the Infected and we have one heck of a story, so here we are, my first Crossover, BEGINS

P/S: Any ideas are appreciated, plus any Parings of different Infected and some Alien's from Mass Effect will be possible, another thing is what Infected will take the place of which Humans in the game, whichever and whenever they may have been born, Enjoy the story!

Prologue: Humanity's Resurrection

-Bzzz- "If you are listening to this, and understand it. Then I am dead… and you did it, sorry, I mean it that way, killing me and… is a good thing, I'm sorry for what you must be feeling now, I will explain the situation best I can, my name is Arnold Rows, I am… was the lead scientist into the research of the Infected, the Infection had spread to even further parts of the world, the military, were not used to the strange talents of the special infected, they were swarmed, over the next twenty years, civilians had tried to stay alive for as long as they could, you probably know this depending on your lives before" -Bzzz-

-Bzzz- "unfortunately, nowhere they could go could escape the Infected, they had been over run, especially since Special's had been producing more lately, eventually, this place became a refuge for the last of the Uninfected, all biologists, scientists, microbiologists, name it, this place had it, but the Infected had an inbuilt radar to find humans, they found this place, despite it being in the middle of a desert, over the course of eight years being here however, we tried to develop a cure, we worked, we tested, we failed… but then we found a way, many protested of course, calling it inhumane and disgusting, it was debated between everyone for a good few months, and then they found us" -Bzzz-

Clang, Clang

-Bzzz- "That's them! Hurry up-" "I know, I know wait want for a second… they broke in in a matter of seconds, cutting through defences like butter, many people died, and now there is only three of us, if any of them are with you, please don't be harsh to them, it was my idea to go through with it" *sobbing* "please calm down Natalia, it's the only thing we can do right now… we developed the cure to curb the animal instinct which drove you to kill, unfortunately… well you probably know now, we also couldn't spread it to the Common Infected because we could only effect the virus through the unique DNA within the Special's blood, we injected it into our own blood stream and we are… waiting for you" -Bzzz-

-Bzzz- "I am sorry to put even more weight on your shoulders, but you now need to go out there to administer the cure to other Special Infected, the Common will ignore you fortunately, just get the Special to bite you and the cure will take effect, after approximately five hours the Green Flu will cease to make them do things they wish not to, it may take a year, five, maybe a decade, but then Humanity will be back on its feet again," "Yeah right, it hardly sounds alive let alone human" "JULIUS, do you have any idea what they could be going through! Shut up!" -Bzzz-

-Bzzz- "Sorry about that, look you are still human, not monsters so get that in your head, you will have all your memories of before you were infected and at worst you will only have fragments of your life after you were, and as for us… we chose to do this you need not mourn over us" -Bzzz-

BANG, BANG, BANG

-Bzzz- "That's a motherfucking Tank man; I don't want to be torn apart by one of those fuckers!" "Then by all means ask him nicely, I'm sure he'd make do by just beating you to death" "Fuck you!" "…also… I should tell you about our families, we had found out that my mother and sister, as well as Julius's brother and Natalia's daughter are Special's, in order are Jemma Rows, Celia Rows, Jamie Forrest and Rachel Carr, I won't be able to say goodbye to them because I have an earlier form of the cure inside me, so I won't come back with it, there's a chance however that Julius and Natalia will become Special's, but in the case they don't… tell their families, as well as mine, we love them" -Bzzz-

CRASH

-Bzzz- "Here they come, you come, good luck, and god bless Humanity, in whatever shape or form" –Bzzzzzzzzzz- "If you are listening to this, and understand it. Then I am dead…

The video played again in the background, the computer had a bloody handprint on it, now dried on the heat of the monitor,

The room was like something out of a horror movie, two bodies were on the floor, ripped apart with limbs scattered around the room, which thankfully was dark enough not to see the scene easily.

The only lighting was from the monitor, as it played on a loop, showing four huddled figures in the room, silent except for the occasional cough and rasping breath to be heard, and looking down at the floor in a circle formation,

The first one wore a black hoody with combat trousers with tape over his clothing holding down the puffier parts of the hoody; his face was covered by his hood with only his lower jaw was showing, sharp teeth were protruding from his mouth and the fingers on his hands had a sharpened, thin look to them, giving them the resemblance of claws,

The second figure had boils taking up half his face, throat and also stopping sight in one eye, it ripped through the clothing of his shoulder and down his left arm, the other side of his face was relatively unscathed as well as his other arm, giving him a two-face like look, but the most distinguishing feature was six tongues sticking out of his head and neck, twitching every now and then creepily, he was also the one who gave of a cough every few seconds to break the silence,

The third was female, with a tattered lab coat being her only form of modesty other than a bra and a pair of panties, she had pale skin that glowed a strange red aura that matched her glowing eyes, she was incredibly thin with bones sticking out, she was the most normal one there but with the exception of long lethal claws that were razor sharp and lay on the ground beside her,

The fourth and final figure was huge, he had bulging muscles, was eight foot tall and five foot wide, in comparison his legs were tiny, as well as his head which seemed to shrink into his body, all over his skin were injuries like cuts and bullet holes and an open sore on the left of his chest, he was leaning on his hands in the stance of a gorilla, his knuckles were swollen that showed he did this often.

They did not know how long they sat there, listening to the infinite loop of the last words of Arnold Rows, it was until another round of coughing from the tongue one did the hooded one look over at him,

"You okay there?" he asked, his voice was scratchy and out of use, likely due to the constant screaming he emitted when he was Infected,

"Just *cough* *cough* about" he finished his bout of coughing and looked around at the others, "normal for a Smoker I suppose, so what's your story?"

"Just a regular guy into parkour, survived for two years before I got bitten and turned into a Hunter, hell knows after that, you?"

"Bet you by four years" the Smoker give a grim smile, one of his boils burst from the movement spewing smoke and pus, he winched from it, "I worked in a garage in Vegas, living the sinful life, smoked too much with people trying to get me off them, if someone mentioned I'd be a ugly zombie because of it I would have listened to them"

"Yeah…wait what do you mean?"

"It seems pretty obvious, I used to smoke, I'm smoking now, I think that's how I turned really, and maybe following the same theory, that is how you zip around rooftops so easily"

The Hunter thought on this, "Sound logic got to admit, what about you two then?" both of them looked at their companions, who looked back at them with bemused faces,

"You just came back to life as a being that ate others as food and you are chatting?" The woman asked,

"Well, yeah, what do you expect, woe is me, I ate a bunch of people and I don't remember it, sure it's tragic, but no use worrying over something we can't remember and has happened a long time ago" the Smoker replied, "My names Jack by the way, Jack Harris,"

"Mines Timmy Cobb and you are Natalia Carr, right?" asked the Hunter

"It's Kinsley actually, I was divorced a long time ago…" she looked into space for a while, "I'm sorry"

"For what?" asked Timmy,

"For all of this… the cure, your appearance-

"Don't be sorry"

Everyone looked at the hulking speaker, who had joined the conversation,

"You made a hard decision, more than I can say about some people in Military, I may not be thrilled being the size of an elephant, but at least I am able to understand what an elephant is"

Natalia was silent for a while, "Thank you"

"No problem and I can't believe I'm saying this, but I hope my own friends are Special Infected, they would probably kill me because I died though" he laughed in a roaring fashion at his inside joke,

"So what do we do now?" Timmy asked,

"What the hell do you think?" asked the Tank as he stood up to his full height, "travel the world, restore people to their former selves, raise a nation from the ashes and find some cigarettes, I went nearly two decades without mine, and after all this, I'm going to need it"

"None for me thanks *cough* I don't want to test it out in this body" Jack said,

As they stood up Natalia looked at the large figure as he made his way to the ripped open doors from his own hands, "But what if they don't accept the change, and think themselves as monsters?"

The Tank stopped at the door and turned his body to face them all,

"Then we'll cross that bridge when we come to it, and I will cross it this time," he smiled in a humourless as the others gave a questioning look at the giant and they all walked into the hallway, Timmy then realised something,

"Wait big guy, what's your name anyway?"

There was a slight pause as they walked down the hall, bodies were littered on the floor, and some were walking around, some looked at the curious group before moving out of their way on the account of a Witch in their presence,

"Me?" the Tank asked as they made it to the exit, they looked out of the door, to see miles of desert in the horizon, another long walk thought the Tank as he continued on,

"I'm a man, who had a handful of medals and a knee full of shrapnel, and my name is William Overbeck, but you can call me Bill"

A/N: So what do you think? I will try to alternate between Massively Slaughtered and this one as much as can depending on the views, yet again, school, the house getting done up, it may be a little delayed, but no need to worry, I will update as often as I can, also, what do you think of Bill coming back? In my opinion it was stupid when they did the whole Sacrifice thing with him, and I thought why the fuck not, let's bring the old guy back, and let the Epicness continue.

-VERY IMPORTANT READ-

Now we got big decisions here, who to bring in, the survivors all died, so no miraculous last human bullshit, it's for my plans in the future rest assured, and what I will bring them back as, any Special you want, shout it, I'll consider, and for anyone you thought Bill would be better as a Hunter or a Charger, lay off, it was the only choice because of the comics, and remember that I will be using both L4D and L4D2 Infected, including the cut Screamer, so wish away, and I will be making every Infected have an increased lifespan to fit into Mass Effect and also bumping up the timeline outside of Earth because of it not being possible to go through an apocalypse and to space in less than two centuries, so watch out for chapter two, see ya!

Next time, the Timeline of Infected Earth.