Telepathy

Perfect information for one mana, and the design proposition is almost comically lopsided: you spend a card slot, and in exchange every decision your opponents make becomes legible. The reason it never broke anything is that it converts information into advantage only if you already have a plan for the information. Knowing the counterspell sits in their hand does not cast your threat into it; it just tells you to wait. The distance between knowing and acting holds the effect in check, which has always positioned the card closer to a control-deck luxury or a combo-deck safety check than to a tempo play. The flavor is clean too: surveillance rendered as a passive enchantment rather than a single peek or a recurring tax. Where Duress strips a hand and Gitaxian Probe glances at it once, this keeps the window open indefinitely, changing the texture of a game more than its math. Your opponents stop being able to bluff, sandbag, or represent answers they do not hold. For decks that win by sequencing around a single piece of interaction, that permanent visibility justifies the slot; for everyone else, it is a card that tells you things you cannot always use.