Warm up cold creatures in the caves. May also be used to snuggle certain skittish creatures who have eaten too much treasure.
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— Item Description
The Comfort Blanket is a resource that can be crafted at the Crystallogy Workbench. There are two recipes for it in that workbench, one to make 5 blankets and the other to make 100 blankets. Throwing these at a critter with a icon above its head will give you Lesser Crystal Caches.