Sinew Dancer

The whole design lives in the gap between two activation costs for the same tap ability. Four mana to tap a creature is a price nobody pays on purpose: a control effect stapled to a one-drop as a last resort, doing nothing worth doing while the game is even. The corrupted line drops that same effect to a single white mana, and the discount unlocks at the poison milestone (three counters on an opponent, the point where the toxic clock has already begun to run). That gap is what the card is built around. It is a repeatable tapper that becomes efficient only after your deck has done its work elsewhere: a payoff wearing filler-creature stats. A one-mana Phyrexian holding down a blocker every turn is a real engine for a proliferate-and-poison shell; the same body in a deck with no poison plan is a 1/1 that can barely function. Corrupted rewards commitment to the poison axis, and Sinew Dancer makes that bargain plainly: the cheap activation is gated behind a condition you control by winning, not by drawing the right answer at the right time. It asks nothing at deckbuilding beyond a wholesale commitment to the toxic game plan, and it pays out only after that commitment has already landed.