Twilight Sparkle finds a spell to create a portal to another world. She and Spike decide to use it to send Discord to another world, one already chaotic as it is, so that he can cause no more damage when she and her friends are gone.
He lands on the strange world of Earth, in a place known as Tokyo, Japan. Once in this new world, he is freed from his stone prison and attempts to rule it, but a large dragon like beast born of radiation is in his way. He needs to destroy this strange beast so that he can take this world for himself.

But wait, there's more!

The monster is not the only thing on this world, there's also the Space Sheriff Gavan (Introduced at end of chapter 1) and Kaizoku Sentai Gokaiger (Pirate Squadron Gokaiger, to be introduced at the end of Discord vs. Uchu Keiji Gavan most likely)