When I first saw it I thought it was a spell that made this creature. Now I see it is a creature that can make more of itself.
In my mind, it works better if it is a spell to begin, like you as the controller of fire awaken this volcano, then the volcano grows. Though, that requires a stone pillar already in play to start off the reaction, nerfing it, but allowing the spell to cost a bit less? Anywhooo....