The Fhtagn are extradimensional eldrtich entities which are able to bend the laws of physics and feed on evil. The vocalizations of the fhtagn are painful to humans, though if you have an evil soul you can withstand them. It's difficult to injure a fhtagn, even for superhumans.
Their appearance is that of a mass of tentacles surrounding a large fang-lined mouth with multiple prehensile tongues and a single telescopic eye-stalk. It's home dimension has not been seen yet, but it likes the bottom of the ocean, an area that is pitch dark, extremely cold, and with a high pressure.