Boa Constrictor

The pump ability folds in on itself in a way the rate quietly depends on: the 3/3 grows to a 6/6 only by tapping, and that tap is the same one an attack would have demanded, so the snake cannot swing the turn it swells. Green of this era could not be trusted with a five-mana 3/3 that became a 6/6 for nothing, and the price is the creature's own offense. The math pays off in narrow, mostly reactive windows. Declare it as a blocker while untapped, then tap after blocks to eat an attacker it had no right to trade with; pump in response to a combat trick or an opposing pump spell before damage, and a body that looked outclassed suddenly survives or kills. Outside those moments the ability is inert, because spending the tap forfeits the attack the creature would otherwise make. It reads like a finisher and plays like a puzzle about when six standing-still power beats three swinging. The answer is rarely, which keeps the snake at the modest end of green's fatty spectrum rather than near its ceiling.