Deathbringer Thoctar

The death-counter engine sits on a body that turns the graveyard into ammunition. Every other creature that dies anywhere on the battlefield offers it another +1/+1 counter, and each counter can be spent for a point of damage at instant speed, which makes the 3/3 a slow-charging cannon that grows in any board state where things are trading. The friction is the conversion rate: one creature death buys one counter, one counter buys one damage, so the engine wants either a steady stream of dying bodies or a single mass death to load it all at once. Pair it with a sacrifice outlet and the trickle becomes a flood of counters you can immediately fire off as a wide reach effect, the Thoctar itself shrinking back to 3/3 as it drains the stockpile into faces and blockers alike. What distinguishes it from later aristocrat payoffs is the open targeting: the damage can hit creatures, planeswalkers, or players, so the same counters that clear a battlefield can also close a game. It is a creature that converts attrition into inevitability, asking only that the board stay busy enough to feed it.