Ethers are very unique from one planet to another. Someone from a different planet may look the same physically, but the ether inside of their body is usually very different. Some planets have a strong ether, such that their inhabitants cannot be harmed physically, mentally, or emotionally. Other planets have an ether that can become subject to the earth's ether.
If you are dealing with an entity who appears to be indestructible, the safest route is to send the spirit back to its "home." "Home" may be another planet, it may be another part of the earth that is unknown, or it may be the abyss. If the entity's home is the abyss, you know that you are dealing with a demon from hell. If you pray in the language of the spirit, from the heart, the indwelling Holy Spirit will know precisely how to deal with each entity.
The Lord God Almighty El Shaddai