Pestilence Rats
A lord effect turned inward: where most "scales with your creatures" designs pump the whole team, this one hoards the bonus into a single body, its power swinging with every other Rat on the battlefield while the toughness stays nailed to 3. That decoupling is the whole math problem. The fixed 3 means the toughness never carries the card; it grows teeth only as the swarm fills out, which makes it a payoff that needs the deck built around it rather than a card that builds the deck. It counts itself out, too: with no other Rats in play it is a 0/3 wall, a deliberate floor that punishes drawing it before the board is set. The conceit traces back to the old common Plague Rats, where each copy grew with every other Rat including its own namesakes, and the gimmick is unchanged: a tribe whose members are worthless alone and lethal in numbers. The flavor and the arithmetic are the same gesture. One rat is nothing; a plague of them ends the board.
