Swarm Culler

The trigger is the wrinkle here: not death, not attack, but the moment the creature becomes tapped. That reframes what the card wants from you. Attacking is the obvious tap, but so is crewing a vehicle, paying a convoke cost, or activating any ability that demands a tap, and every one of those becomes a discretionary sacrifice-and-draw. The 2/4 flying body invites the attack line, but the more interesting builds treat the tap symbol itself as the fuel line, turning routine board activity into card advantage while a spare creature or artifact is on hand to feed it. That "may" clause matters too: the engine never forces you to eat a permanent you cannot spare, so a turn with nothing expendable simply passes without cost. What holds it in check is the four-mana price and the fact that the draw is throttled to one per tap, and only for creatures and artifacts, so it wants a wide, active battlefield to keep the tap events coming rather than spiking into a burst of cards. It reads as a modest evasive body that happens to sit at the intersection of two economies black has long loved: sacrifice value and repeatable card draw, paid for one tap at a time.