
Maybe Big Claws have a less sophisticated type of natural glamour. They can't look like a different shaped creature, like imps, but they can glamour themselves to a different colour so they can hide amongst the ordinary megalocrabs. Some sort of special light, from sprites or fireflies, seems to be the go to glamour dispeller that lets you see the true appearance. Maybe Big Claws are sort of like a chameleon and the sprite cores dispel the colour glamour.