Hired Claw

The whole design is a feedback loop keyed to a single condition: an opponent has to lose life before you can grow the body. The attack trigger is the ignition, pinging an opponent for one whenever your Lizards swing, and once that damage lands the grow ability comes online for the turn. That sequencing is deliberate and self-contained, because this creature is itself a Lizard: swing with it and its own trigger satisfies the "opponent lost life this turn" clause, so it can seed the very condition its activation demands. The once-per-turn cap on the counter keeps the scaling linear rather than explosive, so this stays a slow-building threat instead of a mana sink that runs away in a single turn. What makes the piece cohere is that the two halves lean on each other: without the tribal trigger the activation rarely turns on, and without the activation the trigger is just chip damage on a fragile one-drop. It rewards a board of small Lizards doing repeated combat damage, converting an aggressive tribal curve into direct reach that ignores blockers, then banking that reach into permanent stat growth. A Mercenary that gets paid in the enemy's life total, and only once the invoice is settled each turn.