Criatura — Clérigo humano pirexiano
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Siempre que otra criatura que no sea ficha entre al campo de batalla bajo tu control, prolifera.
You don't have to choose every permanent or player that has a counter—only the ones you want to add counters to. Since "any number" includes zero, you don't have to choose any permanents at all, and you don't have to choose any players at all.