Scurry Oak

Two triggers wired to feed each other is the design puzzle here, and reading the second one carefully is what separates a curiosity from an engine. Evolve wants your later creatures to be bigger; the token trigger wants counters to keep landing. Play it fair and the drip is slow: a larger creature enters, one counter goes on, one Squirrel appears. But the token ability fires on one or more counters being put on the Treefolk, not once per counter, so its real currency is distinct placements: it counts how many separate times counters arrive, not how many arrive at once. String many separate counter-placements together, each from a repeatable source, and each placement mints its own Squirrel. What stalls the loop from within is that the Squirrels themselves cannot restart it: they are 1/1s, and evolve only triggers on a creature with greater power or toughness than the 1/2 body, so tokens never clear the clause. The loop lives elsewhere. Attach an external effect that drops a counter whenever a creature enters (Ivy Lane Denizen is the canonical piece), and now every Squirrel that enters places a counter, which mints another Squirrel, which places another counter. The small stature is what keeps the fair half easy: almost any nontoken follow-up creature clears evolve's power-or-toughness clause, so the trigger rarely misfires. That distance between a modest uncommon ticking up one Squirrel a turn and a genuine combo axis explains why a body this unassuming keeps getting built around.