Raucous Entertainer

The activation restriction is the whole design puzzle: the counter only lands on creatures that entered this turn, so the boost is wasted unless you keep the board refilling. That flips the usual green-counters math. Instead of rewarding a wide, static board the way a card like Cathars' Crusade does, this one wants the tokens to keep coming, turn after turn, so a go-wide engine feels less like a payoff and more like a fuel line: every batch of freshly made creatures gets a permanent bump the moment you fire the ability, but only if it arrives while the ability is still available to fire. Pair it with anything that produces creatures on your own turns and each new arrival can gain a size once you tap it, then holds that size for good. The tap symbol usually limits it to one activation per turn cycle, which keeps a single counter-doubling loop from spiraling, and the cost is cheap enough that the tax is really just the tempo of holding one mana open. It is a token-swarm accelerant built to reward sequencing your creature drops around a single window rather than dumping the hand at once, and the reward is that the whole day's production keeps its bonus forever.