The Eyedol is a critter that only spawns in the Brimstone Crag. It can be caught using the Bug Net or Golden Bug Net to be carried around in the inventory and released later, or crafted into a Eyedol Cage or a Eyedol Statue to be placed as an animated furniture item. It cannot be released once crafted. It also has a rarer gold counterpart.
The Eyedol will stay stationary and monitor the player's movements in a similar fasion to the Ashen Monolith.