Roaring Primadox

The bounce trigger is mandatory and unconditional: every upkeep, a creature you control goes back to a hand, and the only choice is which one. Left to its own devices, the cleanest target is the Primadox itself, which means recasting a 4/4 for four mana with nothing to show for it. The point is to never let it come to that. Built around enters-the-battlefield value, the trigger becomes a free, recurring reset for any body whose arrival you would happily replay: a draw, a removal pulse, a tutor, a token-maker. Send a fresh creature back and you reload whatever it did on the way in. The constraint is that the trigger never stops and never picks for you, so the deck has to supply a creature it genuinely wants returned each upkeep, or the engine starts eating its own board. That same requirement doubles as maintenance: a creature you bounce dodges what was coming for it, though anything that exists only as a token simply vanishes the moment it would touch a hand and cannot be returned this way. Note the timing, too. The ability resolves at the beginning of your upkeep, on your schedule rather than in response to a threat, so it is a clock to plan around, not a reactive escape hatch. It belongs to a small green family that turns one-shot ETB value into a repeatable clock, and it asks the least to assemble, because the trigger fires on its own instead of waiting on an activation.