Anonymous, I don't understand what your argument is. You think it should cost more because in order to have enough attack to be effective with liquid shadow, it would need a ton of poison counters that kill it immediately when you cast liquid shadow?
You are aware that poison counters don't increase its maximum hp, only it's health regeneration, right?
Forest Spirit/Spectre costs 2 and 3 and can grow +2|+2 each turn without any other cards, and it's hp increases as well.