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"Fair is foul, and foul is fair / Hover through the fog and filthy air. . ."  "Double double, toil and trouble." (Macbeth)
Moral ambiguity, seeking to inflict trouble on the mortals around them. 

The wayward sisters of Macbeth. They who insinuate and suggest, working for the downfall of the kingdom and not just Macbeth, who is merely a pawn in the larger picture.

Ambition, arrogance and greed destroys Macbeth and his wife. It is a choice the would-be king made that Banquo did not.