Untamed Kavu

The kicker cost is the whole design argument. Spend nothing and you have a two-mana 2/2 with vigilance and trample, a tidy early body that both blocks and swings without penalty. Add three mana on the way down and the same creature arrives as a 5/5 with those same two keywords, a five-mana threat that lands at a point in the game where a flat green vanilla body would only embarrass you. The card is built to read as a fine turn-two play and a fine turn-five play, with the only difference between the two being whether you had spare mana lying around. That is precisely the pitch kicker was invented to make: not a modal fork between two effects, but one creature that scales with how much of your turn you can afford to spend on it. Delivering the growth through +1/+1 counters rather than a printed size bump has a real consequence, because those counters are permanent and stack with anything else that pumps the board, so a kicked Kavu keeps everything it gains and can grow past 5/5 from there. Vigilance and trample are what justify paying for the bigger frame: a 5/5 that attacks without tapping down and pushes damage through chump blockers is doing exactly what a green curve-topper is supposed to do, which is close the game before the opponent gets a turn to stabilize.