Anim Pakal, Thousandth Moon

The engine runs on a feedback loop that most token-generators only gesture at: every attack grows the counter, and the counter is the multiplier for the next attack's token count, so the Gnome army doesn't accumulate linearly, it compounds. Attack with a single non-Gnome creature and you net one counter and one Gnome. Do it again with that counter in place and you get another counter plus two Gnomes, then three, then four. The tokens arrive already tapped and attacking, so they hit this combat rather than sitting back for a turn; the defending player can still block them, but every unblocked Gnome is damage the swarm didn't have to wait for. The trigger condition is the constraint doing quiet work. It cares about attacking with non-Gnome creatures, so the Gnomes she manufactures can never feed the loop themselves; the growth has to come from the rest of your board declaring attackers, and note that she does not have to swing in herself to fire the trigger, only that something non-Gnome does. A 1/2 that pumps herself while spitting out an increasing swarm sits in a lineage of go-wide payoffs that reward a populated battlefield, but the compounding structure is unusual: the reward for attacking is a bigger reward for attacking next turn, and left unanswered for even a few combats the token count outruns any board a defender can profitably assemble.