From what I gathered, a Planetnik seems to be an air spirit that is somehow associated with Perun, the Slavic god of thunder and lightning. However, my sources are not particularly credible, sometimes contradictory and fail to mention any actual tales featuring the creature.
What exactly is a Planetnik? What does it look like, and what are its main properties? How is one created? What is its relationship with Perun, if any?
This is the abstract a paper published in an (apparently) respectable academic journal (2010): the russian original 'planetnik' is rendered as 'hobgoblin':
In the regions of Orawa and Podhale, among the local elders, beliefs about hobgoblins , able to bring or mitigate thunderstorm, survived up to this day. The hobgoblins are supposed to travel on clouds, perceived as dragons, and depending upon peasants' fulfillment of request for food, or failure to fulfill one, are able to either destroy or protect the harvest. This work discusses features and properties of the hobgoblins, including their relation to the Lateran ringing tradition. The hobgoblins occur also in fiction literature, which enables a discovery of the topos of naming ordinary people "a hobgoblin".
The paper is online in Russian.
