Slith Firewalker

The growth clause is the whole hook, structured as a feedback loop with a single failure point: connect once and the body steps up, then a bigger body connects for more, and the counters compound every turn the defender can't profitably block. Haste turns the loop on early, so the clock starts the turn it lands rather than the turn after. The vulnerability is baked in: it enters as a 1/1, which means nearly anything in red's reach can answer it before the first hit, and a single chump or a piece of removal at the wrong moment resets the entire investment to zero. That gamble is the design: the card asks the attacker to find an open lane immediately, then pays off steadily for getting through, which makes it either nothing or a genuine threat with very little in between. The Slith cycle gave each color its own version of this idea, but the red one inherited haste, the keyword that best fits a creature built to connect before the opponent can set up. As an early-era expression of a snowballing combat creature, its math punishes a slow defense and folds completely to a fast one.