Midnight Reaper

Black has always paid for its card draw in life, but the older designs took the payment as a standing tax: Phyrexian Arena ticks you down every upkeep, Greed asks for a chunk per activation, Necropotence sells you the whole library up front. This converts that tax into a per-death installment plan, dealing you 1 damage whenever one of your own nontoken creatures hits the graveyard and handing back a card in exchange. That the payment is damage rather than a straight life loss is a real wrinkle. The damage comes from the Reaper itself, so any effect that prevents the noncombat damage it deals blanks the cost outright, and giving the Reaper lifelink means each trigger's own damage gains you the life back the moment it resolves, zeroing out the tab without an attack. The nontoken-you-control clause is what keeps it from spiraling: token armies, the natural fuel for any sacrifice deck, draw nothing, and an opponent's creatures dying does nothing for you. The engine wants a board of your own real creatures dying to combat and removal rather than a pile of free bodies generated for the loop, which also defines its company: aristocrat shells that trade bodies for value, go-wide swarms that expect attrition, anything that treats its own creatures as a renewable resource. The 3/2 body matters more than it looks, because a refill engine that sits idle is a liability; this one attacks into the same clock it inflicts on you. The danger is self-inflicted: a board wipe resolves, then each death stacks a separate trigger, and every one deals its damage as it resolves. Draw fast or die to your own engine is the tension the card is built around.