Kalraka Dzeik is a sentient lightning storm with a following of cultists. It has much in common with a natural disaster or a plague; it starts at a single point but spreads like wildfire if given the chance. It is capable of terrible destruction, and will take heroic effort to stop, if it can be stopped at all.
During a storm the PCs come upon a little boy that plays in the rain. Upon further inspection they discover that he has one eye and a long tongue lolling in its mouth. Spit dripping. It is a demon from beyond that can access our realm during storms, it eats all heads that are not its own, living and dead.