This requires you to find an Ice Wand artifact from the Creeping Winter DLC levels or to purchase one from the camp merchants. Now, head into the Radiant Ravine secret level on a really low difficulty so you can easily run through. You are looking for squids that sparkle, these are the glow squids and there should be a couple of them on this level. Line up your shot and use your Ice Wand to kill the glow squid.