A-Heartfire Hero

A zero-power body that wants to be pointed at, then killed. The valiant trigger and the death trigger form a closed loop that flips the usual read on a targeting effect: you are not protecting or pumping this mouse so much as loading it up to detonate. The counter comes once per turn, the first time you aim a spell or ability at it, so the growth is metered rather than explosive; the payoff is that each counter it does collect is a point of damage waiting on the death trigger. The design's cleverness is that it collapses two things a build-around creature usually needs (a reason to target it and a reason its own death matters) into a single card, so the deck's incentives never contradict. It rewards the exact play patterns a low-to-the-ground aggressive shell already runs (combat tricks, activated buffs, sacrifice fodder) and turns removal against its controller: kill it and the counters you fed it come back as reach. Left alone it does nothing on the board, and toughness of 1 makes it trivial to trade with, the pressure valve that keeps a one-mana engine from running away. The line to watch is the one where it never blocks or attacks at all, taking one counter a turn until a sacrifice outlet converts the whole accumulation into a burst of damage to each opponent's face.