Stupefy

Card textReaction[Reaction] (Play any time, even before spells and abilities resolve.) / Give a unit -1 Might this turn, to a minimum of 1 Might. Draw 1.

One Energy, -1 Might, and it replaces itself. A single point decides most combats: it turns a trade into a win, or a 1-Might surplus into a loss for them. It can't take a unit below 1, so it never kills on its own — count the Might before you cast it.