Phyrexian Defiler

The whole body sits behind the activation: tap, sacrifice, and a creature shrinks by three in both directions until end of turn. That makes the 3/3 a removal spell wearing a creature costume, with all the friction and all the flexibility that implies. The friction is real: the ability needs the creature untapped, which usually means waiting a turn for summoning sickness to wear off, and once it fires the body is gone, so the card spends itself to do its job. The flexibility is the payoff. A -3/-3 splits cleanly: it kills a 3/3, it shaves a 6/6 down to a blockable 3/3, and at instant speed during combat it can blow out a trade or save a creature you are worried about. Better still, when the body has already attacked or chipped in damage, that one-for-one stops feeling like one at all; the removal becomes a second life for a creature that already did work. Phyrexian Carriers across this era leaned into the same self-sacrifice idiom, treating their own death as the cost of an effect rather than a downside to mitigate, and this card pushes that idiom about as far as removal can take it: the creature exists to be spent. The reason the rate sits where it does is the tap-and-sacrifice gating; an effect this clean at instant speed would be undercosted if it did not ask for a turn of patience and the permanent itself as ammunition.