Marrow-Gnawer

The exponential is the whole engine here. Tap and sacrifice one Rat to make as many tokens as you have Rats, and because the sacrificed Rat is gone before the ability resolves, the population doesn't just recover, it compounds: sacrifice from a board of four and you make three new tokens for a net gain of two; sacrifice from a board of eight and you make seven for a net gain of six. Each activation widens the base for the next one, which turns a tribal swarm into a self-fueling loop the moment you can untap or copy the activation. The fear granted to every Rat is what closes the gap between the wide board and a dead opponent: a horde of 1/1s that most decks simply cannot block becomes a credible clock rather than a chump-blocking pile. This is a commander built around a creature type that, on the table, is mostly vanilla 1/1s, and the design answers the obvious problem (how do you make a deck of one-power black tokens matter) by making the tokens both the resource and the payoff. Sacrifice them to make more; swing with the survivors; the lost board width on activation is paid back many times over the next turn. The tap cost is the real governor on the loop: one activation per untap, so the engine wants a way around the limiter rather than rewarding a single greedy turn.