Heartfire Hero

The valiant keyword pays off targeting your own creatures, and this mouse turns that reward into a two-sided threat. The +1/+1 counter is the small half; the death trigger is the engine. A creature that deals damage equal to its power to each opponent when it dies inverts the normal calculus of aggressive red: the opponent's removal spell does not answer the problem so much as detonate it, and every counter you have stacked becomes a number pointed at their face. That reframes combat entirely. Blocking is a losing trade, because the block kills it and the damage lands anyway; even a favorable double-block still fires the trigger. The design puts the pilot in control of when the payload goes off: a pump spell that grows the body is also a spell that grows the eventual burn, so a single target on your own turn does double duty. The card wants a shell built to poke it repeatedly, where the counter and the death damage feed the same clock, and it punishes the exact interaction (spot removal aimed at a small threat) that red aggro usually fears most. Handing an aggressive deck a threat that makes the opponent's answers work against them is a rare thing, and this one costs a single red mana.