Iron-Craw Crusher

Two Wurms in one card, and the interesting wrinkle is that the payoff moves with whichever one you paid for. The attack trigger reads current power, so casting the full 4/6 hands an attacker +4/+0, while the cheaper 2/5 line comes down earlier and pumps for +2 instead. That coupling of body size and reward is what makes Prototype more than a discount mechanic here: the decision you front-load (a bigger threat later versus tempo now) also sets the ceiling on the buff, so neither mode feels like a strictly worse version of the other. Toughness stays generous on both sides, which matters because the Wurm is the one throwing the punch: 6 or 5 toughness lets it survive the combat it started rather than trading down after handing out the boost. The pump targets a single attacking creature rather than the team, which keeps it a directed push (best aimed at an evasive threat you want to swing for a lethal chunk) instead of a mass anthem. This is a workmanlike common built to demonstrate the mechanic more than to bend a format around it, but it captures Prototype's cleanest idea: a creature whose size and whose reward scale together, so the mode you choose is the same choice as the payoff you get.