Knight of Obligation

Extort wants a body that stays on the battlefield, not one that threatens to end games, and a 2/4 with vigilance is the toll collector built to that spec. The mechanic is a slow drip: every spell you cast offers the kicker, and the value accrues over a long game rather than arriving in a single burst, so the engine's only real failure state is the creature dying before the game grinds out. Four toughness is the answer to that, ducking under most of the small removal and aggressive bodies that would pick off a flimsier enabler. Vigilance does separate work: it lets the Knight contribute to the red zone and still hold the line back, which matters because Extort triggers off your spells regardless of how the creature is positioned. The trigger is independent of the body's combat status, so the drain fires whether the Knight attacked, blocked, or sat idle. What vigilance actually buys is the ability to pressure an opponent without surrendering a blocker, keeping the four toughness relevant on defense in the same turns it pokes for two. The white side of the Orzhov pairing tends to get the durable, defensive half of the mechanic's enablers, and this is that half: not a clock, but the extort outlet that asks for nothing except to keep standing while you do everything else.