From TVLine.com:
Mirror, mirror on the wall, who’s the most-willing-to-sell-out-their-ally-as-a-corrupt-crook of them all? Find out by watching TVLine’s exclusive first look at this Sunday’s Once Upon a Time (ABC, 8/7c).
Based on this peek at the next episode — which will reveal in flashback the Magic Mirror’s very interesting (and rather familiar) origin — it appears that his Storybrooke alter ego, Sidney, harbors no ill will toward Emma, who recently beat him out for the sheriff’s job. In fact, the Daily Mirror scribe is looking to strike a deal with his former opponent — one that will seemingly help her take the evil Queen mayor down a peg. But is Emma ready to incur Regina’s wrath?
