Friendship is Survival

Also available as a spray image for most Valve games. Should work in L4D and L4D2. Just download the file and import by booting the game and navigate to settings > multiplayer > load custom spray.

Here's an idea, we take humanized ponies, we give them deadly weapons, we put them in the Left 4 Dead universe. Now, how cool is that.

Technically, it isn't really Left 4 Dead because we now have 6 characters, but killing off two of the main cast isn't exactly a very popular idea. That, and you can actually think up interesting gameplay mechanics by using these six characters, emphasizing even more that one needs to cooperate with the other players to get through the game. After all, friendship is survival. It goes a little something like this:

Little warning though; these descriptions are laden with Left 4 Dead terminology. Still, they should make sense to the non-initiated.

Twilight Sparkle is the de facto leader of the group and being a powerful magician, she's a deadly character in the hands of a skilled player. Twilight has a special melee attack that recharges over time. Once fully charged, Twilight can use her powerful telekinesis to levitate and throw the same objects the tank is able to manipulate, except with greater accuracy. However, this is at the expense of her overall physical ability; being such a neeeeerd her running speed is much lower, jumps only as high as necessary for the game and has average aim and slightly longer reload times when handling weapons. Twilight is a character that needs a bit of cover, but becomes a valuable ally when faced with big hordes or special infected, especially when fighting a tank.

Applejack is the muscle of the group, specialized for fighting infected at close range. Obviously prefers a shotgun when controlled by a bot, a weapon equally suited for close encounters. Applejack's melee attacks are very powerful, capable to shoving away hordes with ease and with little fatigue. Applejack is also the only character that will actually punch and kill a singled out common infected, which makes her more ammo-efficient. Her overall physical abilities are slightly higher than most characters, but it's at the expense of her handling of non-shotgun weapons, making her a very poor character for long-distance attacks.

Rarity is the answer to Applejack's shortcomings. Rarity's job is to keep infected far, far away and prefers the sniper rifle, a precision weapon for a woman as sophisticated as she is. Also, being a "unicorn", she's the only character that can detect and pick up items from a long distance, making her a very convenient character for getting items that would normally require a nasty detour, particularly when it comes to health items. It almost goes without saying that the dainty lady isn't exactly the fastest and strongest of the bunch, although slightly more fit than Twilight. You do not want to have her fight a horde on her own, give her breathing room to do her job. Also, her high accuracy with the sniper rifle or the hunting rifle is nowhere to be seen with the shotguns, which she handles slowly and clumsily. She handles the other guns a bit better, but it's still below average.

Rainbow Dash is the rusher's wet dream. Rainbow Dash is all about speed and, well, speed. Rainbow's running speed is well above that of the others and prefers the M16 assault rifle; quick and easy. Rainbow Dash is the only character that can outrun the Witch and an excellent character to troll the crap out of the slow Tank, making her a great distraction for Twilight's telekinesis. Her speed and agility goes at the expense of brute force and weapon accuracy; she aims like shit and can become troublesome when caught in the horde. Also, because of her speed, she becomes more vulnerable to sneaky special infected preying on lone wolves.

Pinkie Pie is the everywoman of the group without any particular special abilities like the other characters, which in turn makes her a valuable asset to the group, since she can work with just about anyone. Pinkie is of average strength, speed and doesn't show a particular advantage or handicap when handling weapons. Pinkie is there to assist the character that needs it at the moment, whether it is covering Twilight as she's levitating a car, or helping AJ shove away a horde. As a bonus, since she's an engineerin' "earth pony", her favorite melee weapon is the chain saw, which she can run about 50% more efficient than her team mates, making her a true killing machine when equipped with one. Also, she's the Ellis of the group as she will tell random "Keith" stories at the most inappropriate of times.

Fluttershy is arguably the toughest character to mold into the Left 4 Dead franchise for rather obvious reasons. It's almost unthinkable to have a character like her in a situation as cynical as a zombie apocalypse. But she still got her close friends, reason enough to survive this mess.
Playing as Fluttershy means that you play a support role, as you play a relatively fragile woman who used to be afraid of her own shadow. Being a "pegasus", you are less affected by gravity and able to jump higher and further than the other characters, making you invaluable to retrieve characters that are behind points of no return. Also, years of taking care of sick animals are paying off as she is very quick at helping up incapacitated teammates and healing them. This could mean the difference between life and death.
Generally speaking, Fluttershy has about the same characteristics as Pinkie Pie, physically. Her major drawback is that her handling of guns comes with an above average recoil, which makes burst-firing crucial for remaining accuracy, but this does reduce her kill rate. Also, as we all know, Fluttershy isn't exactly known for speaking loudly, which makes it easy for your teammates not to notice when you yell "_Reloading!".

And that pretty much covers it. Oh yea, and there's the campaign poster that I drew, you may have noticed it. It was a nice experiment with the coloring and the overall composition of it all. And it was a nice excuse to do a bit of Rule of Cool.

Also, commenting with proposed in-game lines is highly encouraged. Constructive criticism is appreciated, too, of course.