unkillabe dragon Eyialah

I was palying a random map that has had dozens of named drakes like this which were virtually invincible.  However, later in the game I have found a surefire way to destroy them (although it seems a bit ridiculous and I wish there were other ways like using a company of soldiers or something of the like).  You need to hit them with damage that is "undefendable".  The only source that I have found however is the special attack from a dragon...  So um...you might be "dodging" them for awhile.

I think hurl boulder is undefendable... but uh... good luck with that,