Kristin Bauer Kristin Bauer

Once Upon a Time there was an Evil Queen — but she wasn't the only evil force in all the land.

This Sunday's episode of Once will introduce the self-proclaimed Mistress of All Evil, Maleficent (True Blood's Kristin Bauer). In the original Sleeping Beauty story, Maleficent is the vengeful fairy who casts a spell upon Princess Aurora, causing her to fall into a deep sleep after being pricked by the spindle of a spinning wheel. 

In the world of Once, however, Maleficent is an old frenemy of the Evil Queen (Lana Parrilla). "Maleficent is almost like a big sister to the queen," Parrilla teases. "She's taught her some tricks and they probably have created spells and curses together, so you will see that on some level."

ABC's Once Upon a Time turns fairytales into reality

However, her arrival isn't pleasant. "When Maleficent goes to visit her, it's not necessarily coming from a friendly place," Parrilla says. "Maleficient wants something from her."

What, you ask, does she want from the Evil Queen? That will be answered in Sunday's episode of Once at 8/7c on ABC. Until then, hit the comments with your theories.