So, I had this idea floating around in my head for a crossover, if anyone wants to have a crack at it. Here is my summary.

The Creator believes that Celestia has crossed the line with her invasion of Earth. However it is unable to interfere with mortal affairs itself, so it sends someone who can. But who it chooses will make Celestia, and Equestria as a whole, wish it came itself. For who it sends, will turn Equestria into a world of fear. The Creator has sent the King of Terror himself, It has sent King Ghidorah. Because, sometimes, it takes a monster to stop a monster.