Written by Sharktopus117, and set after the events of Season 3, this crossover between My Little Pony: Friendship is Magic and Godzilla starts out with yet another battle between Godzilla and King Ghidorah. During the battle, King Ghidorah is sucked into the Dimension Tide and transported to Equestria where he is drained of his powers by Celestia. However, as more and more kaiju begin to leak into Equestria, Ghidorah must make a choice; add Equestria to his unending list of planets he has stripped bare of life or become its reluctant protector. Can be found here.
Fan Fic / Misadventures Of King Ghidorah In Equestria