Setting her sights on Equus as her next conquest, Maleficent, mistress of all evil, frees the dreaded king Sombra. Renewed and wielding a new power—and with a growing army of Heartless at his command— Sombra and Maleficent work to bring darkness to Equestria and eventually the whole world. But the ponies will not face this threat alone.

Yen Sid, sensing the evil that seeks to consume this peaceful land, enlists the help of two keybearers to travel to this new world and stop the Heartless before the world is lost to them.

Crossover with Kingdom Hearts. Rated Teen just to be safe.