From the preview:
Hey Wyrdos! The first Monday of September is upon us, as well as a preview of a new Neverborn model! The Adze is from the newest book, Broken Promises. Let's learn a little more about where these monsters come from!
When a Will o’ the Wisp has fed upon enough blood, it matures into an Adze. Traditionally, this took decades, as the Gremlins and other swampfiends that the Wisps fed upon provided it with little nourishment. Something about human blood, however, triggers a greatly accelerated growth process in the Wisps.