This story is copied straight from FiMFiction, please check there for a better summary. This is the gist: the keepers of the Elements of Harmony, Spike, Derpy Hooves, and my main OC from "Shisno Chronicles: Friendship is Magic" are transported into the TF2 universe. There, they meet a member of the Story Crew and are taken into the fight between RED and BLU. Non-canon to SC:FiM.

The discovery of an extensively useful element brings about a gigantic scientific leap in Equestrian technology. Seeing the potential of owning the largest reserves of this material, an Equestrian entrepreneur 'hires' a team of mercenaries that can conquer their enemy's territory - and protect their own. Little do they know, the richest ponies of Equestria have all done the same.