Applejack finds a strange visitor in her apple orchard one day, with even stranger stories to tell...
MLP/L4D2 crossover. My first story on FiMfiction.net! May add more tags as story progresses.
Credit for the image goes to brokencreation on DeviantArt.

Twilight Sparkle believes she has perfected a process to allow Earth Ponies and Pegasi to teleport. Unfortunately, in the Land of Ooo, a bubblgum-haired princess is about to run a similar experiment. Will even all of the friendship in Equestria be enough to settle Finn down? Will Pinkie Pie ever get her doughnut? Perhaps along the way, everyone will learn that truly, friendship is ALGEBRAIC!

After a brief spat with Spike over a seemingly trivial matter Twilight decides that in order to learn more about dragons she should try to become one. With a simple spell she transforms her little pony self into a larger dragon and quickly realizes that she has no way to change back available to her....

Part 1: Lyra's Pyro Predicament
Part 2: Twilight's Demoman Devastation
Part 3: King Sombra's Robotic Retaliation

When a mishap causes two para-dimensional weapons to colide with one another, RED Team's Pyro is sent flying from the Team Fortress 2 universe into the alternate universe of My Little Pony, where he is almost instantly discovered by Lyra, who shelters him in her home.

Having him hidden in her small townhouse isn't easy; keeping him from setting things on fire, teaching him that not every cart that passes by is cause for alarm, and that blue ponies are not something to be suspicious of.

However, with Nightmare Night soon approaching, Princess Luna feels that there may be something more sinister riding on the coat tails of Pyro's grand entrance; the first human to ever set foot in Equestria some thousand years ago...