A wretched entity of the frozen lands, the WinterKill is the remnant of a mortal left to die in despair and endless cold.
Where the ships float, empty, and the ocean lay wide and empty, where the northern lights shine and the winds chill live the Gesthari. Wraithlike predators who ride the storms.
The counter to the effects of the Barrenfield Oaks. It converts sunlight into the ingredients necessary for a healthy soil.
The local band of 'nasties' (goblins / orcs / whatever) lives in relative peace with the local population.
Along come the PCs and go through their usual heroic monster bashing routine, wiping out the nasties and pinching all their stuff, then continue on their way.
Problem is, they don't kill ALL he nasties. The survivors want revenge and, after spending a few months recovering, start to take it in their own inimitable style (which is not unlike that of the PCs come to think of it).
Next time the PCs are in the area they find themselves VERY unpopular with the townsfolk.