Imposing Sovereign
Tempo as a static effect. The point of this little Human Noble is not its 2/1 body but the tax it levies on the opposing board: every creature an opponent commits enters tapped, which means no fresh blocker and no surprise attacker either, since a tapped creature cannot attack no matter what keywords it brought with it. Haste, in particular, becomes a dead word. That converts cleanly into the resource a white aggressive deck values most, which is unanswered combat steps. A creature that cannot block until its controller's next untap is functionally a turn behind, and against a board developing one creature per turn that delay compounds: the aggressor keeps swinging while the defender is always one body short of a wall. It is the design ancestor of Thalia, Heretic Cathar, which later widened the same idea to lands and stapled it to a relevant body, but the pure version here is sharper precisely because it asks nothing in return: no upkeep, no trigger, nothing to answer except the creature itself. The fragility is the price. A 2/1 dies to nearly everything, and once it leaves play the effect simply stops applying going forward (the creatures already tapped untap normally on schedule), so the card asks only that it stay alive long enough for those one-turn delays to stack into a lethal clock. A clean statement of a recurring white-weenie principle: deny the defender his reactions and let the math do the rest.

