flashfly Cage is a Palico Gadget in Monster Hunter World (MHW).
A Palico gadget that stuns monsters with a flash of light. They can use this more often as their proficiency increases.
How to get flashfly Cage
This Palico Gadget is obtained by completing the Grimalkyne sidequest in the Ancient Forest.
You can begin the sidequest by traveling to the top of the Ancient Forest with your Palico in tow. In the maze of vines and pathways behind the Rathalos nest, you will encounter a lone Grimalkyne, who will run away from you. Follow him all the way to his encampment, and he will reward you with the Flashfly Cage.