After a thrilling adventure with their Smurf friends in New York City, all the ponies want is a nice vacation with their families before they head back on their Unity Quests. But as their vacation is just getting started, they are once again called by the Unity Crystals on another mission where the mortal world and Equestria hangs in the balance.

This time, they join Mystery Incorporated and some new friends in Japan for a special martial arts competition, where the ghost of the Black Samurai races against them to possess an ancient sword, the Sword of Doom, which is believed to possess incredible powers.

But through a series of twists and turns, they discover that Misty's mother Paradise Moonray has a hoof of her own in this evil scheme, hoping the Black Samurai will be able to help her return to and conquer Equestria for her own malicious reasons.

Now, it'll take the Mane 6, Shaggy, Scooby, the rest of Mystery Incorporated and some very special new friends, including figures of legend, to put a stop to the villains' wicked plans, find the Sword of Doom and save the mortal world and Equestria from falling into the wrong hands and hooves.

In the end, our heroes will learn that loyalty, honor and courage may be their only key to stopping evil and unlocking the answer to the mystery.

(S2E5 of G5 Adventures)