Clement, the Worrywort

The bounce clause is written as a descending ratchet rather than an engine that spirals out of control: it can only return a creature you control with strictly lesser mana value than the one that just entered, so each link in the chain rebuys something cheaper than the last, never something equal or larger. That ceiling on target size is what keeps the trigger an engine instead of an infinite loop. Every creature you play (including additional bodies feeding the "another creature you control" clause) offers to send a cheaper creature back to hand, so a board full of enters-the-battlefield triggers becomes a recurring stream of recasts: a one-drop dork returns to be replayed, a two-drop rebuys the one-drop again, and each recasting refunds tempo through the mana half of the card. That second ability is the quiet enabler, and its restrictions matter: only Frogs you control gain the mana ability, and the mana pays only for creature spells. The payoff is therefore narrower and more deliberate than a generic value engine. You want a wide bench of cheap Frogs specifically, because those are the bodies that both trigger the bounce and fund the recasts it enables. The result is a self-contained green-blue creature loop whose ceiling scales with how numerous and how cheap your board is rather than how large any single piece grows. The vigilance is nearly incidental, a nod to the frog holding the fort while the value accrues behind it.