Hex is average on it's own, great with status, allows for party members to work together (another mon opens with thunder wave, for instance?), and unlike shadow ball, comes into the picture early. As in, wild Yamask and Litwick will usually come with Will-o-wisp and hex. Shadow ball is a high level move, and late game TM. Also, burn isn't a bad status to inflict anyway, seeing as it cuts attack. Helps Litwick survive and lets Yamask tank to silly levels. And of course, don't forget STAB can bring you to power 150.
Of course, my big advice to would-be Hexers: watch out for Guts.
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