Board Thread:Questions and Answers/@comment-24693225-20140318225913/@comment-24145588-20140318231400

You can never place Ethereal monsters in the breeding structure on any of the Natural islands, so the only way to get more than one Ethereal there is by the 4-element/3-element breeding combos, or by purchasing them with diamonds.

But, once you get multiple monsters on the Ethereal Island, you will be able to start breeding them there. You can never place two monsters of the same type in the Breeding Structure together (on any island), but many times on Ethereal Island, whatever combination you put in the Breeding Structure will not produce the hybrid, and the "failure" will give you a copy of one of the parents. That's an easy (but not entirely predictable) way to get multiple single-element Ethereals.

For example, I've been trying for about a week to get my first Arackulele, and have instead bred a boatload of Grumpyres and Reebros (which I have sold off for dog food).