These are large land bound crablike creatures about the size of Grizzly Bears. Physically, they are quite tough… and strong. The fact that they travel in pods of 4 to 12 allows them to be even more formidable. They live partially in the astreal plane, which allows them to support the weight of their shell (and makes them hard to target).
Their food is concentrated magical energy. They can sense it at huge distances. Since spells and such are hard to eat (being in motion) and magical places are the equivalent of a sea of krill to them, they are looking for magic stashed in concrete places. Their primary food source is magic items, alchemical potions, and enchantments.
These creatures see obstacles between them and a good food sources as trivial. They have the strength and the pseudo claws to stop just about any creatures that might get in its way and demolish trees, walls, and other standing objects that are “in the way”. They can even tunnel through soft earth at a suprising fast (slow walking rate) clip. Sure they will sometimes “go around” things. However, if they are “hot on the scent” of food, a straight line is the best path.
While eating the magic, they do a pretty good job of mangling/ eating the physical aspect of said items in the process of chowing down.
Given the dangerous nature of these creatures, it is good they only lay an egg once every few years.
These things will be the bane of dungeons everywhere, as they will slowly eat away much of the treasure (and the magical traps… so it can be advantageous to follow these things).
They will attack people with highly magical natures (i.e. high magic powers). They will probably kill the person in the process of sucking out the power.