(I wanted to get in here first before my brother so I did, take THAT Aldrin!)
Telekhine - Percy Jackson
Telekhines are mysterious smiths and sea demons native to the islands of Keos and Rhodes. They are the children of Thalassa and Pontus.
Telekhine's don't really do much, in all honesty. All they do is forge weapons, but in a swarm - they are lethal little things.
I would love to give your more information, I really do, but so little is known of them, it's harder than you think.
They are at least seven feet in height and live (weird isn't it, giving a Demon a home...) in Mount Etna.
They are all male, but they have no need to reproduce, they are immortal. But you can kill them ... of sorts...
Weapons and Powers:
Weaponry - none. (Damn I need to find a Demon which uses a weapon...)
Powers - a few.
They can use magic, and they did, several aeons ago. They created a mix of River Styx water and sulfur, which killed plants and animals.
So, they can kill....they just use magic, which is kind of cool ... in a creepy way...
How to Kill:
I mean it! Grab a grenade, make a volcano explode, anything you can. It's the most efficent way to kill them. But since they're immortal, they kinda keep coming back, but you'll be fine, once you've killed seven rounds of these things, you'll be perfectly fine.
Blow them up, is my final advice.