Rancor

The recursion clause is the whole trick. A +2/+0 trample buff for one mana is unremarkable on rate; what makes the design endure is that the enchantment never dies for good. Pay the green mana again each time, and you own a permanent threat-amplifier that survives chump blocks, sacrifice effects, and most spot removal aimed at the creature underneath it. Kill the wearer and Rancor floats back to hand, ready to suit up the next body in the queue. That single bounce trigger converts an aura, normally the most card-disadvantageous way to pump a creature, into a recurring resource that trades up against removal instead of getting two-for-oned by it. The trample is the other load-bearing word: it turns the +2/+0 into reach over blockers, so a board full of small green creatures stops being a wall problem and becomes a clock. Green's aggressive enchantment-aura design has circled back to this template for decades, but the bounce-on-death mechanic has rarely been priced this cheaply or attached to this clean a stat line. It is the rare aura that aggressive decks are happy to run as a four-of precisely because the usual downside, getting blown out when the host dies, simply does not apply. Strip away the era it came from and the lesson holds: the cost of an aura is the risk of card disadvantage, and Rancor's whole design is the removal of that risk.