I was thinking that devourers would be like walking nothing, as they passed through something it would be destroyed, and if someone touched it they would be seriously burned. They would look like monsters made of smoke, with some flashes of red in them, ( Have you ever seen sheet lightning? ) And again only energy beings can harm them. While they feed on material by passing through it and destroying it, they are attracted particularly to energy which is radiated most by energy beings. Um... so that is the basics right now.