Kavu Titan

Kicker exists because of this card, more or less: Invasion built a whole mechanic around the idea that a spell could have a cheap floor and an expensive ceiling, and Kavu Titan is the cleanest demonstration of why that idea works. Pay two mana and you get a serviceable 2/2 to hold the early game. Pay five and you get a 5/5 trampler that pushes damage past blockers, all from the same card. The elegance is that you never hold a dead draw at either end of the curve: the early-game beater and the late-game finisher live in one slot, and you decide which one you cast based on how much mana you have untapped. That flexibility is what kickers buys, and it is why the card stayed relevant long after most green two-drops of its era faded. A floor that trades into anything and a ceiling that closes games is the kind of curve insurance that aggressive green decks have always wanted; later cards like the kicker creatures of Dominaria revisited the same template, but the Titan's split (small enough to play turn two, large enough to matter turn five) set the proportions everyone else worked from.